Update cleanup tasks to only happen on failure

To reduce noise in logs and job overhead only collect last effort debug
info when jobs fail. This should make jobs run more quickly and keep
logs cleaner.

Change-Id: Id62986e5801ddbb46665985766f93a34b462c321

playbooks/base-test/cleanup.yaml

@@ -1,13 +1,16 @@
 - hosts: all
   tasks:
-    - name: get df disk usage
-      raw: df
+    - name: Gather debug info on job fail
+      when: not (zuul_success | bool)
+      block:
+        - name: get df disk usage
+          raw: df
 
-    - name: get df inode usage
-      raw: df -i
+        - name: get df inode usage
+          raw: df -i
 
-    - name: get l2 networking
-      raw: ip link
+        - name: get l2 networking
+          raw: ip link
 
-    - name: get l3 networking
-      raw: ip addr
+        - name: get l3 networking
+          raw: ip addr