Bug 955789 - Enabling mongo connection check in oo-accept-broker

https://bugzilla.redhat.com/show_bug.cgi?id=955789

Re-enabling mongo connection checks in oo-accept-broker.  Without these
enabled, if the broker cannot communicate with mongo you would get odd
error messages from oo-accept-broker
<broker> Bug 956351 - Add mongo rubygem dependency, docs

At least three scripts - broker-util/oo-admin-chk, broker-util/oo-admin-fix-sshkeys, and broker-util/oo-stats - use the OpenShift::DataStore API for performance reasons, and so still depend on the mongo rubygem. This change adds the gem dependency back to the broker Gemfile and specfile.
Move Runtime::Cartridge to openshift-origin-common
Merge pull request #2288 from detiber/bz955789

Merged by openshift-bot
Merge pull request #2292 from dobbymoodge/mongo-BZ956351

Merged by openshift-bot
Merge pull request #2293 from ironcladlou/dev/v2carts/cartridge-common

Merged by openshift-bot
fix bug#958320 - no singleton cart's hook for scaled gears