Increase fullstack job's timeout

It seems that recently we are often timing out the fullstack job when
it's executed on some busy node. To avoid that, lets give 20 more
minutes to the timeout of the fullstack jobs.

Change-Id: I37ec0ba04bafb3b7baec6003155b7d9c43092667
(cherry picked from commit 3354b43)

Author: slawqo

zuul.d/base.yaml

@@ -58,6 +58,7 @@
 - job:
     name: neutron-fullstack
     parent: neutron-functional
+    timeout: 9000
     vars:
       tox_envlist: dsvm-fullstack-gate
       Q_BUILD_OVS_FROM_GIT: False