Update avi_azscaleset.tf

remove 16.04 Ubuntu version with the 18.04 as the 16 does not work anymore.

Author: itlinux

examples/azure/cluster_stages/5_avi_azure_availability_set/avi_azscaleset.tf

@@ -55,7 +55,7 @@ resource "azurerm_linux_virtual_machine_scale_set" "terraform_scale_set_v1" {
   source_image_reference {
     publisher = "Canonical"
     offer     = "UbuntuServer"
-    sku       = "16.04-LTS"
+    sku       = "18.04-LTS"
     version   = "latest"
   }
 
@@ -112,7 +112,7 @@ resource "azurerm_linux_virtual_machine_scale_set" "terraform_scale_set_v2" {
   source_image_reference {
     publisher = "Canonical"
     offer     = "UbuntuServer"
-    sku       = "16.04-LTS"
+    sku       = "18.04-LTS"
     version   = "latest"
   }