Add sec-grp-rule for ipv6-icmp to enable ping6 between instances

The tempest testcase test_network_v6 checks if an ipv6 ping
between instance is possible. But therefore no security-group-
rule is being set up, to allow such a ping. The test fails.

This issue does not apply to a test that runs with the cirros
image, as cirros does not have ipv6 utils installed. There is
a if clause in the testcase, that skips this ping if the util
ping6 is not available.

Change-Id: Ia3fbe771cde8893e9eb3fc43b187435bd0dd1dbf
Closes-Bug: #1417584
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index 5b092c3..a081883 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -907,6 +907,11 @@
             dict(
                 # ping
                 protocol='icmp',
+            ),
+            dict(
+                # ipv6-icmp for ping6
+                protocol='icmp',
+                ethertype='IPv6',
             )
         ]
         for ruleset in rulesets: