Split the merger into a separate process

Connect it to Zuul via Gearman.  Any number of mergers may be
deployed.

Directly find the pipeline for a build when processing a result,
so that the procedure is roughly the same for build and merge
results.

The timer trigger currently requires the gerrit trigger also be
configured.  Make that explicit inside of the timer trigger so
that the scheduler API interaction with triggers is cleaner.

Change-Id: I69498813764753c97c426e42d17596c2ef1d87cf
diff --git a/doc/source/zuul.rst b/doc/source/zuul.rst
index d71912c..ee70523 100644
--- a/doc/source/zuul.rst
+++ b/doc/source/zuul.rst
@@ -83,21 +83,49 @@
 """"
 
 **layout_config**
-  Path to layout config file.
+  Path to layout config file.  Used by zuul-server only.
   ``layout_config=/etc/zuul/layout.yaml``
 
 **log_config**
-  Path to log config file.
+  Path to log config file.  Used by all Zuul commands.
   ``log_config=/etc/zuul/logging.yaml``
 
 **pidfile**
-  Path to PID lock file.
+  Path to PID lock file.  Used by all Zuul commands.
   ``pidfile=/var/run/zuul/zuul.pid``
 
 **state_dir**
-  Path to directory that Zuul should save state to.
+  Path to directory that Zuul should save state to.  Used by all Zuul
+  commands.
   ``state_dir=/var/lib/zuul``
 
+**report_times**
+  Boolean value (``true`` or ``false``) that determines if Zuul should
+  include elapsed times for each job in the textual report.  Used by
+  zuul-server only.
+  ``report_times=true``
+
+**status_url**
+  URL that will be posted in Zuul comments made to Gerrit changes when
+  starting jobs for a change.  Used by zuul-server only.
+  ``status_url=https://zuul.example.com/status``
+
+**url_pattern**
+  If you are storing build logs external to the system that originally
+  ran jobs and wish to link to those logs when Zuul makes comments on
+  Gerrit changes for completed jobs this setting configures what the
+  URLs for those links should be.  Used by zuul-server only.
+  ``http://logs.example.com/{change.number}/{change.patchset}/{pipeline.name}/{job.name}/{build.number}``
+
+**job_name_in_report**
+  Boolean value (``true`` or ``false``) that indicates whether the
+  job name should be included in the report (normally only the URL
+  is included).  Defaults to ``false``.  Used by zuul-server only.
+  ``job_name_in_report=true``
+
+merger
+""""""
+
 **git_dir**
   Directory that Zuul should clone local git repositories to.
   ``git_dir=/var/lib/zuul/git``
@@ -110,32 +138,10 @@
   Optional: Value to pass to `git config user.name`.
   ``git_user_name=zuul``
 
-**report_times**
-  Boolean value (``true`` or ``false``) that determines if Zuul should
-  include elapsed times for each job in the textual report.
-  ``report_times=true``
-
-**status_url**
-  URL that will be posted in Zuul comments made to Gerrit changes when
-  starting jobs for a change.
-  ``status_url=https://zuul.example.com/status``
-
-**url_pattern**
-  If you are storing build logs external to the system that originally
-  ran jobs and wish to link to those logs when Zuul makes comments on
-  Gerrit changes for completed jobs this setting configures what the
-  URLs for those links should be.
-  ``http://logs.example.com/{change.number}/{change.patchset}/{pipeline.name}/{job.name}/{build.number}``
-
-**job_name_in_report**
-  Boolean value (``true`` or ``false``) that indicates whether the
-  job name should be included in the report (normally only the URL
-  is included).  Defaults to ``false``.
-  ``job_name_in_report=true``
-
 **zuul_url**
-  URL of Zuul's git repos, accessible to test workers.  
-  Usually "http://zuul.example.com/p".
+  URL of this merger's git repos, accessible to test workers.  Usually
+  "http://zuul.example.com/p" or "http://zuul-merger01.example.com/p"
+  depending on whether the merger is co-located with the Zuul server.
 
 smtp
 """"