Removes stale DHCP and L3 namespaces. The cron runs once in 12 hours.
Network namespace cleanup is implemented as a daemonset as Kubernetes
does not have a cronjob that works like daemonset-cronjob.
Network namespace cleanup should run on all nodes where DHCP and L3
agents run.
Change-Id: I7525e493067669026e0d57889a3e3238a2bd1308