set default auth_strategy to keystone

Like in change Ife63dc7ab680fcf0588d95c98fc9f29901485c64 for Nova
the default for auth_strategy should be keystone instead of noauth.

Change-Id: I53da5a4b2291a92e56c2e642f8ec38489ea6efc0
Merge "set default auth_strategy to keystone"