Add early failure detection for tempest base job

Zuul can do better resource allocation if it learns early that a job
will fail even when tests haven't completed yet. This is done by adding
a regular expression that will match on a single failing test within a
tempest run. The regex is copied from what the zuul project has already
been using successfully for some time.

Change-Id: I8c9488a55d04e32384d1523a9658a8711b05c340

zuul.d/base.yaml

@@ -12,6 +12,10 @@
     timeout: 7200
     roles: &base_roles
       - zuul: opendev.org/openstack/devstack
+    failure-output:
+      # This matches stestr/tempest output when a test fails
+      # {1} tempest.api.test_blah [5.743446s] ... FAILED
+      - '\{\d+\} (.*?) \[[\d\.]+s\] \.\.\. FAILED'
     vars: &base_vars
       devstack_localrc:
         IMAGE_URLS: http://download.cirros-cloud.net/0.6.2/cirros-0.6.2-x86_64-disk.img, http://download.cirros-cloud.net/0.6.1/cirros-0.6.1-x86_64-disk.img