Wait for cluster to settle in yum_update.sh

Wait for cluster to settle in yum_update.sh

Occasionally we hit "Error: unable to push cib" during update. This is
probably due to the fact that when we try to replace cib in
yum_update.sh, services on the previous updated controller are still
coming up and changing cib, and racing/conflicting with the cib push
from yum_update.sh.

This commit adds waiting for the cluster to settle before exiting from
yum_update.sh, to avoid this kind of conflict.

Also a check for cib-push success is added, to make the update fail
properly instead of hanging indefinitely as we've observed with this
issue.

Change-Id: I953087e0e565474ac553fd57bea2459d2e3a6081
Closes-Bug: #1527644