Add cloud monitoring

Pass: http://jenkins.rackops.org/job/cookbook-rackspace_memcached/16/consoleText

This branch does *not* introduce a dependency on rackspace_cloudmonitoring to the cookbook. Rather, the monitors.rb from this branch is meant to be included from a rolebook's monitors.rb if that rolebook uses MaaS. It should be included after cloudmonitoring::agent is and before cloudmonitoring::monitors is. I didn't add documentation to the README yet, but will do so once this is merged.