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