Make nova-api use servicegroup.API.service_is_up().

Fix bug 1168861

Change-Id: I38e06c8832ec054755daa70898a303383557041b
(cherry picked from commit 616e5d965bd8a2923f00ba4ff194e6a6ee2468cd)
Merge "Make nova-api use servicegroup.API.service_is_up()." into stable/grizzly