Make functional tests more reliable

Regularly failing tests:

• BadSiteUnitTest: LOG_ERROR is not defined - test rewritten
• BadSiteUnitTest: ZAP_HUD_FILES is not defined
• BadSiteUnitTest: Expected condition failed: waiting for element
• FramesPageUnitTest
• PageAlertsPageUnitTest: 100 <1> but was: <0> - hopefully fixed?

Some of the functional tests (tutorial) fail sometimes, e.g.:

org.zaproxy.zap.extension.hud.ui.firefox.badsite.BadSiteUnitTest > cannotAccessApiKeyWhenLoadingUtilsAsScript(FirefoxDriver) FAILED
    org.openqa.selenium.JavascriptException: ReferenceError: LOG_ERROR is not defined
    Build info: version: '3.13.0', revision: '2f0d292', time: '2018-06-25T15:24:21.231Z'
    System info: host: 'travis-job-acbae740-7b82-4d89-9d65-e682edd3a1f2', ip: '127.0.1.1', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-101-generic', java.version: '1.8.0_151'
    Driver info: org.openqa.selenium.firefox.FirefoxDriver
    Capabilities {acceptInsecureCerts: true, browserName: firefox, browserVersion: 64.0, javascriptEnabled: true, moz:accessibilityChecks: false, moz:geckodriverVersion: 0.23.0, moz:headless: true, moz:processID: 5738, moz:profile: /tmp/rust_mozprofile.RP2aKE..., moz:shutdownTimeout: 60000, moz:useNonSpecCompliantPointerOrigin: false, moz:webdriverClick: true, pageLoadStrategy: normal, platform: LINUX, platformName: LINUX, platformVersion: 4.4.0-101-generic, rotatable: false, setWindowRect: true, timeouts: {implicit: 0, pageLoad: 300000, script: 30000}, unhandledPromptBehavior: dismiss and notify}
    Session ID: ad53072a-f6f6-4e5e-a008-bf11c07ff06c
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
        at org.openqa.selenium.remote.http.W3CHttpResponseCodec.createException(W3CHttpResponseCodec.java:187)
        at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:122)
        at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:49)
        at org.openqa.selenium.remote.HttpCommandExecutor.execute(HttpCommandExecutor.java:158)
        at org.openqa.selenium.remote.service.DriverCommandExecutor.execute(DriverCommandExecutor.java:83)
        at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:548)
        at org.openqa.selenium.remote.RemoteWebDriver.executeScript(RemoteWebDriver.java:485)
        at org.zaproxy.zap.extension.hud.ui.firefox.badsite.BadSiteUnitTest.cannotAccessApiKeyWhenLoadingUtilsAsScript(BadSiteUnitTest.java:132)

org.zaproxy.zap.extension.hud.ui.firefox.badsite.BadSiteUnitTest > cannotAccessApiKeyWhenLoadingUtilsAsScript(FirefoxDriver) FAILED
    org.openqa.selenium.TimeoutException: Expected condition failed: waiting for element ([[FirefoxDriver: firefox on LINUX (66975787-1a03-4eae-b8d0-8a28b235e83f)] -> id: left-panel]) to become stale (tried for 20 second(s) with 500 milliseconds interval)
    Build info: version: '3.13.0', revision: '2f0d292', time: '2018-06-25T15:24:21.231Z'
    System info: host: 'travis-job-9f26b00f-c973-416a-a13c-86c968b31ddd', ip: '127.0.1.1', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-101-generic', java.version: '11.0.1'
    Driver info: org.openqa.selenium.firefox.FirefoxDriver
    Capabilities {acceptInsecureCerts: true, browserName: firefox, browserVersion: 64.0, javascriptEnabled: true, moz:accessibilityChecks: false, moz:geckodriverVersion: 0.23.0, moz:headless: true, moz:processID: 5516, moz:profile: /tmp/rust_mozprofile.3VCarq..., moz:shutdownTimeout: 60000, moz:useNonSpecCompliantPointerOrigin: false, moz:webdriverClick: true, pageLoadStrategy: normal, platform: LINUX, platformName: LINUX, platformVersion: 4.4.0-101-generic, rotatable: false, setWindowRect: true, timeouts: {implicit: 0, pageLoad: 300000, script: 30000}, unhandledPromptBehavior: dismiss and notify}
    Session ID: 66975787-1a03-4eae-b8d0-8a28b235e83f
        at org.openqa.selenium.support.ui.WebDriverWait.timeoutException(WebDriverWait.java:81)
        at org.openqa.selenium.support.ui.FluentWait.until(FluentWait.java:271)
        at org.zaproxy.zap.extension.hud.ui.uimap.HUD.openUrlWaitForHud(HUD.java:160)
        at org.zaproxy.zap.extension.hud.ui.firefox.badsite.BadSiteUnitTest.cannotAccessApiKeyWhenLoadingUtilsAsScript(BadSiteUnitTest.java:127)

org.zaproxy.zap.extension.hud.ui.firefox.tutorial.FramesPageUnitTest > testSidePanelsHiddenAndRevealed(FirefoxDriver) FAILED
    org.opentest4j.AssertionFailedError: expected: <false> but was: <true>
        at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:38)
        at org.junit.jupiter.api.AssertFalse.assertFalse(AssertFalse.java:40)
        at org.junit.jupiter.api.AssertFalse.assertFalse(AssertFalse.java:35)
        at org.junit.jupiter.api.Assertions.assertFalse(Assertions.java:185)
        at org.zaproxy.zap.extension.hud.ui.firefox.tutorial.FramesPageUnitTest.checkPanelHidden(FramesPageUnitTest.java:147)
        at org.zaproxy.zap.extension.hud.ui.firefox.tutorial.FramesPageUnitTest.testSidePanesHidden(FramesPageUnitTest.java:153)
        at org.zaproxy.zap.extension.hud.ui.firefox.tutorial.FramesPageUnitTest.testSidePanelsHiddenAndRevealed(FramesPageUnitTest.java:108)

org.zaproxy.zap.extension.hud.ui.firefox.tutorial.PageAlertsPageUnitTest > testTaskAndNextButton(FirefoxDriver) FAILED
    org.opentest4j.AssertionFailedError: expected: <1> but was: <0>
        at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:54)
        at org.junit.jupiter.api.AssertEquals.failNotEqual(AssertEquals.java:195)
        at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:184)
        at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:179)
        at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:508)
        at org.zaproxy.zap.extension.hud.ui.firefox.tutorial.PageAlertsPageUnitTest.testTaskAndNextButton(PageAlertsPageUnitTest.java:100)

(The above stack traces might not be exactly the same in develop, but the assertions should be the same.)

[psiinon]

Just added a checklist to the first comment

[thc202]

The change in #425 addresses a failure in FramesPageUnitTest that happened when waiting for the panels to be hidden/visible (because of the overlap it could open the Alerts dialogue instead of pressing the button to hide/show the frames).