Cleanup and more tests for db.api methods

New tests for methods:

 backup_*
 quota_*
 reservation_*
 snapshot_*
 transfer_*
 volume_*

Removed unnecessary methods:

 quota_usage_create
 volume_metadata_get_item
 snapshot_metadata_get_item
 volume_type_extra_specs_get_item
 exact_filter

Improved coverage of existing tests.

Improved ModelsObjectComparatorMixin.

blueprint: db-api-tests

Change-Id: Ia2a3845f27a7b4b08fd8a16c6010513d213e642f
Drop conf_key_mgr warning message!

By default ConfKeyManager logs tons of WARNING message stating
that it isn't production ready...

Given that it is currently the only Cinder key manager option
which can be used/selected I don't think repeatedly logging
warnings is helpful. Lets just drop the warning message
for now and when a good "production ready" cinder key manager
implementation is implemented perhaps we can re-add a warning to
this class (hopefully making the production ready impl the default).

Change-Id: Id1fdddc20a963f9fa4749ad57f355cd83d0e14e3
Closes-Bug: #1236459
Ignore H803 from Hacking.

H803 checks for a period in commit messages, something the community
clearly rejected as a sensible check: periods in commit messages
should neither be rejected or required.

Change-Id: I754e10ca01b3e6f8c6482e1bcd4c2e2ca8c1cfc9
Merge "Ignore H803 from Hacking."
Merge "Drop conf_key_mgr warning message!"
Merge "Cleanup and more tests for db.api methods"