Fix prechecks of a vip address

In the case of a single node environment without haproxy, the var
"kolla_internal_vip_adress" in global.yml should be the ip address
of the host. However, the prechecks will fail, because this ip
address is used by the host node and is pingable.

This commit fixes the prechecks of a vip address properly.
When the var "enable_haproxy" is "no", this fix will skip prechecks
for a vip address.

Change-Id: I0b752f179d20f82e3d6331047ee0bd802ab99a4b
Closes-Bug: #1570935

ansible/roles/prechecks/tasks/port_checks.yml

@@ -439,6 +439,7 @@
     - "{{ kolla_internal_vip_address }}"
     - "{{ kolla_external_vip_address }}"
   failed_when: ping_output.rc != 1
+  when: enable_haproxy | bool
 
 - name: Checking if kolla_internal_vip_address is in the same network as network_interface on all nodes
   command: ip -4 -o addr show dev {{ network_interface }}
@@ -446,3 +447,4 @@
   changed_when: false
   failed_when: "'169.254.' not in kolla_internal_vip_address and \
                 kolla_internal_vip_address | ipaddr(ip_addr_output.stdout.split()[3]) is none"
+  when: enable_haproxy | bool