Refactor init_nova() and init_cinder() to simplify Grenade upgrades

* Glance: create_glance_cache_dir()
* Cinder: create_cinder_cache_dir() and create_cinder_volume_group()
* Nova: create_nova_cache_dir() and create_nova_keys_dir()
* Random tidy-up changes

Change-Id: I20d995d4c2e5facfb912ee03a6cda6c56f20bbe9
Merge branch 'init-split' into dt-test
Merge branch 'nova-config-cleanup' into dt-test
Merge branch 'database-service' into dt-test
Merge branch 'clean-ex' into dt-test