HA for MongoDB

Hrm, we never merged the code in roxy :/

So this is https://github.com/crowbar/barclamp-ceilometer/pull/103 and https://github.com/crowbar/barclamp-ceilometer/pull/119 with some cleanups, for stoney.
The reason it's here, and not on line 23 is that it's a safety net in case the search doesn't return anything. It's the same thing we do (although in a different way) in the `common.rb` recipe.