Add a QuotaClient and quota API tests

This change adds a QuotaClient for testing the Barbican quota API.
It adds a quota test suite and integrates the QuotaClient with the
plugin testing infrastructure.

Change-Id: I3249fb879f519da63129e0ec5117377a21094974
Depends-On: I813648476a3a7b0b0e416a524d4629dffe36c92e
Implements: bp tempest-plugin
5 files changed