Scope requests to horizon scoped region
Scope requests to horizon scoped region

Instead of adding region to all requests by default if not
specified, we'll instead honor a region of 'INJECT_REGION'.
This is because not all environments add region as a dimension
for metrics, so we can't do this by default.

Change-Id: I126cd604b3b6d84d0f4efa5dc99aa538e6cf0d77
Closes-Bug: #1494337

stackforge/monasca-ui,openstack/monasca-ui,stackforge/monasca-ui,stackforge/monasca-ui,openstack/monasca-ui,openstack/monasca-ui,openstack/monasca-ui,stackforge/monasca-ui