Use configured endpoint instead of hardcoded ones

Usage of public endpoints was hardcoded
- for the Heat client
- in a test for the Zaqar client
- when checking if a service is available

A test also required Heat to be configured to use public endpoints when
talking to services. This test is more relaxed now.

Change-Id: I3784e126d28a51d990702e1b9e6bf23f0447fa21
4 files changed