Support for alternative image names

It allows to publish the Docker image under more names, e.g. publish the image with specific version and latest tag at once.

Support for older Docker versions

Support for Docker versions that don't support --password-stdin switch for docker login command.

Add standard labels to the Docker image

Standard labels

* provide standard labels for Docker image #1

* perform docker login only if username is provided

* show exceptions from tests

* try to fix test failing on TravisCI

* disable problematic assertions

* different test of docker inspect output

* intentialy break the test

* fix the test

* more stable tests

* test the GitExecutor

Use Java 8u161 where possible

And bunch of small improvements.

Start with empty Dockerfile

0.9.2

start with empty Dockerfile

Image can be removed after publishing

0.9.1

removeImage option added

Initial release

0.9.0

rename the plugin for Gradle portal