Support for creation of v6 subnet and allocation of v6 ip address.
Addition ipv6 family in schema for InterfaceRouteTable
Update static route provisioning script for v6 family.
Addressed review comment to use __contrail_exception

Change-Id: Ibc0d67f2e6136c786a2b79455eef1ec61d788fe7
Merge "Support for creation of v6 subnet and allocation of v6 ip address. Addition ipv6 family in schema for InterfaceRouteTable Update static route provisioning script for v6 family. Addressed review comment to use __contrail_exception"