Fix gearman installation.

Remove 'include' gearman as it's redundant and results in:

  "Error 400 on SERVER: Duplicate declaration: Class[Gearman]
   is already declared;"

Also, move declaration to zuul manifest as it is part of the
configuration of the OpenStack zuul server.

Change-Id: I9acf0b0d5e6b8c83aca38aa6b201eddf6ea5f023
Reviewed-on: https://review.openstack.org/26264
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins