Move SERVICE_PROTOCOL from stack.sh to stackrc

This ensures that SERVICE_PROTOCOL is available to other consumers
of the devstack environment like grenade.

Change-Id: I702d7d239e50dd1446d55c076c7a7c57768486ff
Closes-Bug: 1335953
diff --git a/stackrc b/stackrc
index a05fc18..9701d2d 100644
--- a/stackrc
+++ b/stackrc
@@ -431,6 +431,9 @@
 # Undo requirements changes by global requirements
 UNDO_REQUIREMENTS=${UNDO_REQUIREMENTS:-True}
 
+# Allow the use of an alternate protocol (such as https) for service endpoints
+SERVICE_PROTOCOL=${SERVICE_PROTOCOL:-http}
+
 # Local variables:
 # mode: shell-script
 # End: