update-agent: wait for pods to terminate before rebooting
update-agent: wait for pods to terminate before rebooting

This change makes the agent wait until all pods are terminated before
rebooting. Prior to this change, the agent would reboot immediately after
the pod delete request was made and, consequently, pods were not
given the time needed to terminate gracefully.

sdemos/container-linux-update-operator,sdemos/container-linux-update-operator