GCE is the only "simple" driver since it turns out every other cloud
is not simple enough. The state machine driver interface is just
as simple (perhaps simpler) and can accomodate a variety of clouds.
This ports the GCE driver to the statemachine interface and drops
the simple interface entirely.
Change-Id: Icfc298d83750ca31503211f920900d9207488bc2
adab6eeb0d