Get rid of pennyworth dependency in the machinery VMs

We now use a static SSH key for inspecting the subject VMs from within
the machinery VMs, so we don't need pennyworth to upload the dynamically
generated keys anymore. The static key is now imported from the host
system to the subject VMs instead.
Merge pull request #28 from SUSE/review_140804_use_static_ssh_key

[Review] Request from 'aduffeck' @ 'SUSE/machinery/review_140804_use_static_ssh_key'