cephadm: switch snmp class to use daemon_to_container function

cephadm: switch snmp class to use daemon_to_container function

Switch the snmp daemon type class to call daemon_to_container instead of
get_container in the class's container method. This breaks a dependency loop
between the class and the get_container function hopefully enabling future
clean ups and code moves.

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