Orchestration tests to use admin user, demo tenant.

Heat tests have unique credentials requirements, so the identity admin
tenant cannot be used.

These requirements are:
- (username=admin) must be an admin user with authority to create
  other users
- (tenant_name=demo) tenant must have a private quantum network
  with dhcp enabled

Change-Id: I1e9a541ac46cd50faeb8f59196b6e17e202135c1
Merge "Orchestration tests to use admin user, demo tenant."