Editable default quota support for cinder

Implement blueprint edit-default-quota

DocImpact

Using the class quotas named `default` as the default editable quotas.

We can use the following cinderclient command to update default quota:

cinder quota-class-update default <key> <value>

Change-Id: I9f97506b41157066026dd43163ec4b1827d5b9cf
Merge "Editable default quota support for cinder"