Exclude remote file systems from inspection of unmanaged files

Remote file systems are all file systems which are mounted either via NFS or
CIFS, directly or via the auto mounter. These file systems are not extracted
by the unmanaged-files inspector. The mount points of remote file systems are
stored as entry of type 'remote-dir' in the unmanaged-files scope in the
system description.
I would rather test the parse function. Then the stubbing here is not needed. This makes the test more robust as it doesn't depend on the implementation of how to get the file content.