Deprecate DATABASE_TYPE and use_database

Select a database by adding it to ENABLED_SERVICE like all
of the other services.  This greatly simplifies using the lib/*
functions in places other than stack.sh

Change-Id: I967e44603b4d69d5d70e1a75a9938172ca434025
Clean up configure_nova() a bit

Change-Id: I2228221051a5a4413a34ca359856d90794fce69a
Refactor init_nova() and init_cinder() to simplify Grenade upgrades

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

Change-Id: I20d995d4c2e5facfb912ee03a6cda6c56f20bbe9
Exercise cleanups

Change-Id: If873d633e31621695a38165b62e854e6d9474d10
Merge branch 'init-split' into dt-test
Merge branch 'nova-config-cleanup' into dt-test
Merge branch 'database-service' into dt-test
Merge branch 'boot-vol' into dt-test