Split up stop_nova to match start_nova

Split stop_nova into: stop_nova_compute and stop_nova_rest. This is
needed to support the partial-ncpu grenade test where we want to stop
everything but nova_compute.

Change-Id: I6a21821277e56897d705ca5746806e2211632d12
Rename all Savanna usages to Sahara

There are several backward compatibility nits.

Change-Id: I93cac543375896602d158860cc557f86e41bcb63
Merge "Split up stop_nova to match start_nova"
Merge "Rename all Savanna usages to Sahara"
Merge branch 'master' of https://github.com/openstack-dev/devstack