Allow a user to disable MongoDB journaling

Allow a user to disable MongoDB journaling

By default MongoDB enables a journaling system that prevents loss of
data in case of an unexpected shut-down. When journaling is enabled,
MongoDB will create the journal files before actually starting the
daemon[1].

The journaling feature is useful in production environment, but not
really on a CI-like system, where we only want to make sure MongoDB is
setup correctly and running, hence here we allow a user to
enable/disable MongoDB journaling.

[1] http://docs.mongodb.org/manual/core/journaling/

Change-Id: I0e4e65af9f650c10fdf5155ff709b4eb984cf4e1
Closes-bug: #1468246