Skip FROM images which are referred to by a named alias

[davoustp]

Fixes #1443
Image alias check was performed only for the FROM <alias1> AS <alias2> case and not for straight FROM <alias1> case.

Signed-off-by: Pascal Davoust pascal.davoust@enghouse.com

[rohanKanojia]

@davoustp : Could you please add a line to doc/changelog.md regarding this change? I think we can proceed with merge after that

[davoustp]

Sure - did not see that (I supposed the changelog was automatically generated).
Process to do that from your point of view? Just commiting the change to my own repo enough? Or do you want me to squash the two commits together and force it upstream?

[rohanKanojia]

Right now we're maintaining a changelog file: https://github.com/fabric8io/docker-maven-plugin/blob/master/doc/changelog.md

You would need to update it linking the bug you're fixing in 0.36-SNAPSHOT section.

[davoustp]

Done.