Tests: Allow multiple machine 'flavors'.

So that not all machines that are used in a test case need to be
identical.

* File names have been changed to include the flavor.
* Most scripts take a "--flavor" argument.
* Setup instructions are factored out of testvm into their own little
  scripts.
Tests: Add 'snapshot' option to vm-run.

Running a machine in snapshot mode is useful for debugging.
Tests: Support fixed MAC for a test machine flavor.
Tests: Test against a real FreeIPA instance.