Add force flag when cleaning up generated files

Under certain catastrophic failure scenarios the expected puppet
generated content may be missing from the local directory when `vagrant
destroy` is run. In this unfortunate circumstance our destroy middleware
can make actually destroying the broken image difficult by erroring when
attempting to clean up the files. Adding the :force option to the remove
commands suppresses all StandardErrors that might otherwise be thrown.

Change-Id: I959e3629dad4ebc6f0cafd9344ead2a60cb5e1d5
Merge "Add force flag when cleaning up generated files"