Instead of having cells service started for every api samples test,
whether or not it is used, only start it on test_cells. This saves
some setup / teardown time, and makes things a bit more explicit.
It also removes the cells service from service listing for a couple of
api samples (az and hosts). That's more indicative of what people will
see in real systems as cells is still a minority and experimental
deploy option.
Change-Id: Ie6d7e8978fd2b3441a141c69d4191266d76e7327
7974f83743