Disable mongo journaling on devstack and Jenkins

The Mongo journal files are taking up a lot of disk space on Jenkins workers and in devstack.  This PR provides an option to disable journaling in these environments.

According to the [docs](http://docs.mongodb.org/manual/reference/configuration-options/#journal), you need two options to disable journaling on 64-bit systems:

    journal=false
    nojournal=true

I also noticed that the `browsers` task was included in the Jenkins worker, leftover from devstack changes, so I removed it.