Python2/3 compatibility for "http" service plugin

Hi there,

while looking into #436, I found the http service plugin would croak on Python 3 saying Cannot GET http://example.org/: expected string or bytes-like object:

mqttwarn --plugin=http --data='{"message": "Hello world", "addrs": ["GET", "http://example.org/", null]}'

2020-08-31 20:14:59,395 INFO     [mqttwarn.commands        ] Running service plugin "http" with data "{'message': 'Hello world', 'addrs': ['GET', 'http://example.org/', None]}"
2020-08-31 20:14:59,397 INFO     [mqttwarn.core            ] Successfully loaded service "http"
2020-08-31 20:14:59,397 DEBUG    [mqttwarn.services.http   ] *** MODULE=/Users/amo/dev/daq-tools/sources/mqttwarn/mqttwarn/services/http.py: service=<mqttwarn.core.Service object at 0x10a7dceb0>, target=mqttwarn, addrs=['GET', 'http://example.org/', None]
2020-08-31 20:14:59,404 WARNING  [mqttwarn.services.http   ] Cannot GET http://example.org/: expected string or bytes-like object
2020-08-31 20:14:59,404 INFO     [mqttwarn.core            ] Plugin response: False

With kind regards, Andreas.

cc @mortenf

[jpmens]

http.py is an absolute mess IMO. I think we should consider replacing its innards with requests. It means an additional import, but it would result in cleaner and portable code.

[amotl]

Hi again,

the patch at #523 might resolve this problem on Python 3. Official support for Python 2 will be dropped anyway.

With kind regards, Andreas.