Quotas by Volume Type

Added a new flag: quota_volume_types

This is a list of volume type names to track quotas for. New resources
are created for volume_<vtype> and gigabytes_<vtype>.

These are persisted in the config file under the keys:
quota_volume_<vtype> and quota_gigabytes_<vtype>.

Another patch will have changes to cinderclient for setting project
quotas by volume type.

blueprint quotas-limits-by-voltype

Change-Id: I88261676edcd6eb5b7cea40654a931f32c00815c