Fix instructions for installing ceilometer controller on SUSE based distributions

Because MongoDB is not available in Cloud:OpenStack:Juno it is necessary
to add an additional repository first.

Also the systemctl commands for openSUSE are missing at the moment.

Change-Id: Ibfdb933da0adc6921c1235f9c577bdfef57ff81e
Merge "Fix instructions for installing ceilometer controller on SUSE based distributions"