Make quotas APIv2 extension use Quotas object for create/update

This makes the quotas extension use the Quotas object for the
create/update operations instead of direct database access.

Related to blueprint compute-manager-objects-juno

Change-Id: Ia2db239d721c9ea680e11409e5eefc59e0dee941
Make quotas APIv3 extension use Quotas object for create/update

This makes the quotas extension use the Quotas object for the
create/update operations instead of direct database access.

Related to blueprint compute-manager-objects-juno

Change-Id: I74295a6f8ebca46421eafedbb28e677d2361c2b8
Method to filter non-root block device mappings

Adding a generator that would provide a non-root block device
mappings, when it's optional variable exclude_root_mapping is
set to true. Otherwise, all mappings will be returned.

The method will be used to handle LXC volumes, as it's root FS
should be handled differently.

Change-Id: I879916021c3b61f19dd69ff11838dbbac19f72d1
Related-Bug: #1269990
Merge "Method to filter non-root block device mappings"
Merge "Make quotas APIv2 extension use Quotas object for create/update"
Merge "Make quotas APIv3 extension use Quotas object for create/update"