API tests for Ironic

Ironic is a baremetal provisioning service that
is intended to replace nova-baremetal-driver.

Recently it was integrated to devstack so now
it's reasonable to start testing it with tempest.

This patch adds a client for baremetal
provisioning service and some tests for the Ironic API.

Change-Id: Ifd65d6a60179e72dbfa81825f234f0ff76ebb055
Merge "API tests for Ironic"