Add a ConsumerClient and consumer API tests

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

Change-Id: I844d1a97ffb82aa67a4ef3b89bd82c90aa221cbb
Depends-On: I930455c6ae1e1127706480f24c0ea46f5cc81e85
Implements: bp tempest-plugin
5 files changed