modified:   Vagrantfile
use smaller clusterhq mongo image
reference clusterhq/mongodb image in place of old mongodb-tutorial image
	modified:   tutorial/Vagrantfile
	modified:   tutorial/volume-application.yml
Merge remote-tracking branch 'refs/remotes/origin/master' into mongo-tutorial-vagrantfile-383
We don't need vagrant-cachier any more.
change references to dockerfile/mongodb image to clusterhq/mongodb
	modified:   volumes.rst
Merge branch 'mongo-tutorial-vagrantfile-383' of github.com:ClusterHQ/flocker into mongo-tutorial-vagrantfile-383
Update exposing-ports.rst

Explain that we're using dev version of mongo
Update exposing-ports.rst
Merge pull request #476 from ClusterHQ/mongo-tutorial-vagrantfile-383

Use new mongo image for tutorial - fixes 383