Accept numeric user and group parameters

`AnsibleModule.user_and_group` will return numeric IDs if no entry exists in `/etc/passwd` and `/etc/group`, but `AnsibleModule.set_owner_if_different` and `set_group_if_different` will not accept numeric IDs- users and groups must exist in the password database.

This PR makes these calls orthogonal, as the output from `user_and_group` can be passed to `set_owner_if_different` and the right thing happens.