(maint) Fix yet another face spec issue.

Commit 275ac959db060f80e4b8635e1213cc0c2255c732 prevented specs
that did 'describe Puppet::Face[...]' from working correctly.
That is because the instance returned for the describe call
would then differ if face_collection_spec is run before the
spec in question.

The fix is rather than clearing all face state, save and restore
the global state before and after all examples.

Also correcting a mistake in indirection_base_spec where a ivar
wasn't being used between the before and after clauses.