Make OSC plugin be able to use glare backend
Make OSC plugin be able to use glare backend

Previously the OSC plugin always used murano as the backend, this commit
adds glare backend to OSC.

Closes-bug: #1626408
Partially implements: blueprint openstack-client-plugin-support

Change-Id: I9efefea422d5d940952eec77afa18913f9cb0b70

openstack/python-muranoclient,openstack/python-muranoclient