Switch the launcher to Gearman.

Remove the Jenkins launcher and add a new Gearman launcher (designed
to be compatible with Jenkins) in its place.

See the documentation for how to set up the Gearman Plugin for
Jenkins.

Change-Id: Ie7224396271d7375f4ea42eebb57f883bc291738
diff --git a/doc/source/index.rst b/doc/source/index.rst
index f901fd0..039cffa 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -10,8 +10,8 @@
 project so that changes are only merged if they pass tests.
 
 The main component of Zuul is the scheduler.  It receives events
-related to proposed changes (currently from Gerrit), triggers tests
-based on those events (currently on Jenkins), and reports back.
+related to proposed changes, triggers tests based on those events, and
+reports back.
 
 Contents: