is_keystone_enabled() was calling is_service_enabled(), which is what called
is_keystone_enabled() in the first place. Make it work as designed and
also change calls to use the full service name. Note that this is all
still comptible with the prior usage of 'is_service_enabled key'.
Change-Id: I9c28377ecf074b7996461d2a4ca12d88dfc4d47e