Add option to report elapsed build times.

The new format will be:
  "http://logs.example.com/6/1/gate/project2-merge/2 : SUCCESS in 00:00:00"

And the option is enabled by default.

Change-Id: Ib50c4948ea0a7b552d46a0e72ecb6c1a9609a771
Reviewed-on: https://review.openstack.org/27570
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins
diff --git a/doc/source/zuul.rst b/doc/source/zuul.rst
index 668bb8f..d79600f 100644
--- a/doc/source/zuul.rst
+++ b/doc/source/zuul.rst
@@ -100,6 +100,11 @@
   git_dir.
   ``push_change_refs=true``
 
+**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
   beginning Jenkins jobs for a change.