Add NoopQuotaDriver

Allows turning quota calls into no-ops, pretending that all quotas are
unlimited.  Useful for child compute cells.

Use by setting this in nova.conf:

quota_driver=nova.quota.NoopQuotaDriver

DocImpact

Change-Id: Id80a89df5ba73db3f5edc05bd0ef4627e9c211fa
Merge "Add NoopQuotaDriver"