Add merge-output-to-logs to base job

This is OpenStack's behavior, and is a decent approach to
interim artifacts for people who don't have a more complex
setup in place.

Depends-On: https://review.openstack.org/629571
Change-Id: If976115957aadb962a8ecb6422595d557b08b54d

playbooks/base-test/post.yaml

@@ -1,6 +1,7 @@
 - hosts: all
   roles:
     - fetch-output
+    - merge-output-to-logs
 
 - hosts: all
   # NOTE(pabelanger): We ignore_errors for the following tasks as not to fail

playbooks/base/post.yaml

@@ -1,6 +1,7 @@
 - hosts: all
   roles:
     - fetch-output
+    - merge-output-to-logs
 
 - hosts: all
   # NOTE(pabelanger): We ignore_errors for the following tasks as not to fail