'IPWrapper.get_namespaces()' is deprecated in version 'Queens'
and was marked to be removed 'Rocky'.
This patch removes it and switches to use
'neutron.agent.linux.ip_lib.list_network_namespaces' instead.
Change-Id: I090cc5841aca5b638d08d65645162811950d6437
Depends-On: Id629481fd722004a7b7d827bf6209785f85f4c64