This patch removes the snapshot/rollback system for the tests and
replaces it with a simple cleanup script that removes the appropriate
files from the VM's $HOME before every test. A side benefit is that
there is no more dependency on the Sahara plugin.
The cleanup script may not provide as good isolation between independent
tests as the previous setup, but it is orders of magnitude faster to run
without a VM rollback for every single test, and it does not break any
of the current tests.
