Improve IPV6 parity in Security Group testcases

This patch implements positive and negative IPV6 testcases
for Security Groups and adds few additional test cases to
validate icmp protocol, remote_group_id and remote_ip_prefix

Change-Id: I3dd272f15a282b2ac58beee10f36c8af66377727
Partially implements: bp ipv6-api-testing-parity
diff --git a/tempest/api/network/base.py b/tempest/api/network/base.py
index 834c010..d9b2848 100644
--- a/tempest/api/network/base.py
+++ b/tempest/api/network/base.py
@@ -83,6 +83,7 @@
         cls.fw_rules = []
         cls.fw_policies = []
         cls.ipsecpolicies = []
+        cls.ethertype = "IPv" + str(cls._ip_version)
 
     @classmethod
     def resource_cleanup(cls):