Removed redundant line from the test.
GRADLE-3141 Attempted to fix the problem with ivy metadata parsing.

It appears that it's possible to create an inconsistent module descriptor model. It is exposed when the same artifacts but with different configurations are added to the model. I fixed the problem where we parse the ivy descriptor. Tidy up is pending.
Renamed the IvyArtifact into IvyMDArtifact to avoid confusion with IvyArtifact type that lives in ivy submodule.
Updated the exception message.
Improved the coverage for the ivy artifact addition to the meta data.