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/tests/fixtures/zuul.conf b/tests/fixtures/zuul.conf
index c031ae3..8948ae8 100644
--- a/tests/fixtures/zuul.conf
+++ b/tests/fixtures/zuul.conf
@@ -1,7 +1,5 @@
-[jenkins]
-server=https://jenkins.example.com
-user=jenkins
-apikey=1234
+[gearman]
+server=127.0.0.1
 
 [gerrit]
 server=review.example.com