CORE-1771 Add ping step to help key acceptance

This commit adds a step where each node is checked for connectivity,
a single node at a time, to enable easier ssh key acceptance if the
user is operating with Ansible defaults to help ensure SSH connection
security.

Change-Id: Ia534b56e496624c4a73bea0dac70a93c107676d4

playbooks/step_ping.yml

@@ -0,0 +1,7 @@
+---
+- name: "Test Connectivity to all hosts"
+  hosts: all
+  serial: 1
+  tasks:
+    ping:
+    where: instance_status == "ACTIVE"

playbooks/update_cloud.yml

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 ---
+- include: step_ping.yml
 - hosts: undercloud
   name: Disable Undercloud
   sudo: yes