Adds horizon snapshot to the controller node

Snapshot 'horizon_installed' will contain the following packages

    1. openstack-dashboard
    2. memcached

This shapshot installs horizon.

This snapshot can be used to obtain stable running version of
controller node and can be used to revert back to this point in case
the students break the cluster.

Change-Id: Ie1c2d1047942db390519f11d233156fea1959a09
Merge "Adds horizon snapshot to the controller node"