engine : rename check_active to make it more generic

Rename check_active to check_create_complete, since "active" is
really a detail of Instance state, and so it seems wrong for other
resources which take a long time to create but are not Instance
based (e.g WaitConditions).  This change will also allow us to
align other stack "state check" functions with the state we're
checking for in a consistent way (e.g check_delete_complete etc)

Fixes bug #1178591

Change-Id: I55a824e6ba3de87cedd0b844e7f4e1294917533a