Added checkpoint parameter to JobTracker.

Now it's possible to set checkpoint=true for the Hadoop framework by
specifying mapred.mesos.checkpoint=true in the Hadoop config.
Added role parameter to JobTracker.

Now it's possible to specify the framework role by setting
mapred.mesos.role.  The default role is "*".
Updated Mesos mapred-site.xml for Hadoop.

Review: https://reviews.apache.org/r/13077