Add a default ignore pattern when dockerFileDir is root project dir

When the dockerFileDir is the same as ${project.baseDir} then it makes sense to have a default exclude for target/** when building the docker image.

[hindsholm]

I also find this quite confusing. I have my Dockerfile in the project root, and I can easily build it with docker build -t some/name . But in order to make this work with docker-maven-plugin, I have to create a .maven-dockerinclude file which IMHO is counter-intuitive. I would prefer that the plugin was more compatible with standard Docker.

[rhuss]

Sure --> https://github.com/fabric8io/docker-maven-plugin/tree/master/samples/smallest or https://github.com/fabric8io/docker-maven-plugin/tree/master/samples/zero-config