Automatically create cluster if it does not exist. Fixes #3

- Also, do not try to drop cluster if resetting when
  cluster does not yet exist.
Sudo as postgresql_admin_user to administer dbs/users.

- Allows for using ident/peer auth method instead of trust.
- Defaults to using domain socket instead of localhost so peer auth works.
Encrypt user passwords by default.
Add {{ ansible_managed }} to templates. Fixes #7