Add GLANCE_SERVICE_PROTOCOL to fix image upload

DevStack change I36fe56c063ca921131ad98439bd452cb135916ac introduced
support for https. This requires us to explicitly set the glance
service protocol in redstack for image uploads to work correctly.
Set GLANCE_SERVICE_PROTOCOL to be http (default), which can be
overridden by setting the environment variable appropriately.

Change-Id: I687486b04939f42f4d9a89da3716e7168f278e8a
Closes-bug: 1374555