clients make heat_url public

Make the heat_url helper function public, so it can be used inside resources
which require a heat endpoint URL, e.g to pass to an instance for signalling.

blueprint: native-waitcondition
Change-Id: If351066e9ad68d2e19dee955d5e9de87f527e17d
stack user add _user_token

Change-Id: I729a6e591e30a93378596eb35722120b4bb364fc
Merge "clients make heat_url public"
Merge "stack user add _user_token"