Only consider common attributes when comparing UnmanagedFileLists

The elements of UnmanagedFileLists (UnmanagedFiles) have different
attributes depending on whether the files were extracted during
inspection or not. That means that a naive comparison between extracted
and unextracted lists will always show all elements as different
although they might actually refer to the same files. This commit
changes this unwanted behavior by only comparing the common attributes.
Do not choke on lacking file lists when rendering unmanaged files scopes

In case of comparisons it can occur that a partial description is
rendered which does not contain a file list at all, so the rendere has
to handle that case gracefully.
Fix empty lines in unmanaged files list when files were not extracted
Add regression tests for recent bug fixes
Merge pull request #382 from SUSE/review_141114_fix_comparing_unmanaged_files

[Review] Request from 'aduffeck' @ 'SUSE/machinery/review_141114_fix_comparing_unmanaged_files'