Ping default gateways before controllers

It may be necessary, in certain situations when using IPv6,
to ping the default gateways first before attempting to
ping other hosts in the validation script.  This swaps the
order of the pings between the controllers and default gateways.

Change-Id: I14b7fcffb0609aee3f0f53150496461396348322
Closes-Bug: 1793598
(cherry picked from commit ae3379e070)
(cherry picked from commit 244b7bf107)

releasenotes/notes/ping-gateway-before-controllers-e029e81961dbaee8.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - Ping the default gateways before controllers in
+    validation script. In certain situations when using
+    IPv6 its necessary to establish connectivity to the
+    router before other hosts.

validation-scripts/all-nodes.sh

@@ -110,8 +110,8 @@ function ntp_check() {
   fi
 }
 
-ping_controller_ips "$ping_test_ips"
 ping_default_gateways
+ping_controller_ips "$ping_test_ips"
 if [[ $validate_fqdn == "True" ]];then
   fqdn_check
 fi