Full class path style configuration of options scheduler_host_manager
and scheduler_driver are deprecated because of dependent changes. This
commit changes the related configurations to use entrypoints in setting
up nova scheduler in devstack.
Related to blueprint scheduler-driver-use-stevedore
Depends-On: I8c169e12d9bfacdbdb1dadf68b8a1fa98c5ea5bc
Depends-On: I3fd42ead44487a21eb5cfaf5a91209277ce30ad0
Change-Id: Iad96c270073b63719237cf9a9aa1c2dc4daa213a
b298e57c9f