Add new scenario test for IPv6 hot plug

This new scenario test is checking if hot plugged IPv6 NIC
can be properly configured with IPv6 address.
It tests both "slaac" and "DHCPv6 stateless" modes.

Change-Id: I7a52feac0f40b7db195bd02db2f364a827364a5e
diff --git a/neutron_tempest_plugin/common/ip.py b/neutron_tempest_plugin/common/ip.py
index 70a3dd5..592f040 100644
--- a/neutron_tempest_plugin/common/ip.py
+++ b/neutron_tempest_plugin/common/ip.py
@@ -117,6 +117,12 @@
         output = self.execute('route', 'show', *args)
         return list(parse_routes(output))
 
+    def get_nic_name_by_mac(self, mac_address):
+        nics = self.execute("-o", "link")
+        for nic_line in nics.split("\n"):
+            if mac_address in nic_line:
+                return nic_line.split(":")[1].strip()
+
 
 def parse_addresses(command_output):
     address = device = None