Installing 'atop' on admin node before deploying HA cluster.

We need to monitor the activity on the Fuel admin node
while HA cluster is deploying.
It will show the health status of the admin node at the
moment of making a snapshot.

Related-Bug: #1289297

Change-Id: I127f92e139fe5131f3080424bd88033ec6e61bbd
(cherry picked from commit a3ff02e7b9866f5912c9e8cb1e540cdd6b71569b)