cephadm: move extract_uid_gid func to container_types module

cephadm: move extract_uid_gid func to container_types module

While extract_uid_gid isn't a perfect fit for container_types it is a
fairly fundamental function for working with containers in cephadm and
doesn't require anything beyond types in containers_types and that
module's existing imports.  Moving extract_uid_gid should allow us to
more easily move other functions in the future.

Signed-off-by: John Mulligan <jmulligan@redhat.com>