Add the ability to consume FakeKeystoneClient class as a client
module. This avoids extra dependencies on the Python mox/mox3
libraries at runtime and allows the end user to wire in the
custom class by simply making the following config setting:
keystone_backend = heat.engine.clients.os.keystone.fake_keystoneclient.FakeKeystoneClient
This use case for this is the TripleO undercloud installer which
uses a heat-all process to transform heat templates into Ansible
playbooks. Previously we leveraged a "fake_keystone" service
as multiple applications and binaries required keystone dependencies.
(Both Heat, os-collect-config, and some openstackclients wanted
a fully version of keystone running)
Now that we've streamlined these dependencies allowing heat to use
a fake KeystoneClient library shim instead of the full fake_keystone
process is much lighter and avoids the security concerns of the extra
socket. This patch allows us to do all of this without installing extra
test time dependencies on mox/mox3.
Change-Id: I03f1789957ba157871fd13164592116d7fcdabe4
Closes-bug: #1723639
14b0451fc9