The ceilometer module checks that the pymongo package is installed on RHEL. It really should be checking for what provides pymongo, and the installed python-pymongo package would satisfy that. So to avoid http://projects.puppetlabs.com/issues/5831 just avoid 'pymongo' disparity on RHEL. Note for >= Havana python-pymongo will be available.
Proposed fix: https://review.openstack.org/#/c/45889/ --> https://github.com/packstack/puppet-ceilometer/commit/a908469b2
*** Bug 1006422 has been marked as a duplicate of this bug. ***