VMware: Remove tests for None in fake._db_content['files']

This looks like a legacy. _db_content['files'] is always initialised,
and checking it for None distracts from what is actually being tested.

This was also the only use of NoFilesFound, so we remove it entirely.

Change-Id: Ided6c71b68a654476512016ddf886e895d75e571
Merge "VMware: Remove tests for None in fake._db_content['files']"