(MODULES-3332) Correct target validation

[hdeheer]

The check should not warn when fragment target is based on concat_file name instead of path.
Previous fix only specifically fixed the case:

concat_file {'a_file': path => '/some/path'}
concat_fragment {'foo': target => '/some/path'}

But it introduced warnings for the case:

concat_file {'a_file': path => '/some/path'}
concat_fragment {'foo': target => 'a_file'}

[DavidS]

Thanks, good catch!