Add max-job-timeout tenant setting

This change adds a tenant setting to limit the timeout value a job can set.

Change-Id: I3875e81b1f6a6e059e7eb57362772e3446e8d022
diff --git a/doc/source/admin/tenants.rst b/doc/source/admin/tenants.rst
index 54bc10a..4722750 100644
--- a/doc/source/admin/tenants.rst
+++ b/doc/source/admin/tenants.rst
@@ -163,6 +163,11 @@
       The maximum number of nodes a job can request.  A value of
       '-1' value removes the limit.
 
+   .. attr:: max-job-timeout
+      :default: 10800
+
+      The maximum timeout for jobs. A value of '-1' value removes the limit.
+
    .. attr:: exclude-unprotected-branches
       :default: false