Adding Jabber Plugin

This change adds support for the Jabber plugin so Jenkins can
report results to chat rooms.

This change also fixes a misspelling of trigger in the documentation
of the join-trigger functionality.

Change-Id: I69659b106c6e1730506ee8150df8c07c1be27254
Reviewed-on: https://review.openstack.org/29779
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins