Reduce six name server lines in to three

Reduce six name server lines into three by making portions optional
so the pattern matches when there's data as well as when it's blank.

Author: mjbear

ntc_templates/templates/aruba_aoscx_show_interface_mgmt.textfsm

@@ -29,11 +29,8 @@ Start
   ^\s*IPv6\s+link\s+local\s+address/prefix\s*:\s*$$
   ^\s*Default\s+gateway\s+IPv6\s+:\s+${IPV6_GATEWAY}\s*$$
   ^\s*Default\s+gateway\s+IPv6\s+:\s*$$
-  ^\s*Primary\s+Nameserver\s+:\s+${PRIMARY_DNS}\s*$$
-  ^\s*Primary\s+Nameserver\s+:\s*$$
-  ^\s*Secondary\s+Nameserver\s+:\s+${SECONDARY_DNS}\s*$$
-  ^\s*Secondary\s+Nameserver\s+:\s*$$
-  ^\s*Tertiary\s+Nameserver\s+:\s+${TERTIARY_DNS}\s*$$
-  ^\s*Tertiary\s+Nameserver\s+:\s*$$
+  ^\s*Primary\s+Nameserver\s+:\s*${PRIMARY_DNS}?\s*$$
+  ^\s*Secondary\s+Nameserver\s+:\s*${SECONDARY_DNS}?\s*$$
+  ^\s*Tertiary\s+Nameserver\s+:\s*${TERTIARY_DNS}?\s*$$
   ^\s*$$
   ^. -> Error