Move testinfra validate to run phase

Zuul now supports multiple run playbooks, lets use that over post-run.

Change-Id: Id6d591023ef9b351e08e4260c281d25eec0836cc
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

.zuul.yaml

@@ -2,10 +2,10 @@
 - job:
     name: ansible-role-nodepool-base
     pre-run: tests/playbooks/pre.yaml
-    run: tests/playbooks/run.yaml
-    post-run:
-      - tests/playbooks/post.yaml
-      - tests/collect-logs.yaml
+    run:
+      - tests/playbooks/run.yaml
+      - tests/playbooks/run-post.yaml
+    post-run: tests/collect-logs.yaml
     roles:
       - zuul: openstack/ansible-role-nodepool