Add Machinery::Ui.warn method for printing warnings to the console
Use the same tarball for setting up the machine and the test

For some reason we had two identical tarballs where one was used to set
up a VM with some test files and the other was used to verify the data
in the VM against. Instead we now use the same tarball in both places.
DRY up test by specifying a test subject
Do not choke on filenames with invalid UTF-8 characters

Filenames sometimes contain invalid UTF-8 characters which triggered
encoding exceptions causing the inspection to fail. We now filter those
files and show a warning to the user about the skipped files instead.

Fixes #59
Merge pull request #91 from SUSE/review_140814_do_not_choke_on_broken_filenames

[Review] Request from 'aduffeck' @ 'SUSE/machinery/review_140814_do_not_choke_on_broken_filenames'