The service policies were not taking the default roles work we did
last release into account. This commit changes the default policies
to rely on the ``admin`` role to create and delete services.
Subsequent patches will incorporate:
- domain user test coverage
- project user test coverage
Change-Id: I58bbe6848c9e8e63656a6c706c84d1747c72a71e
Related-Bug: 1804462
Closes-Bug: 1804463