Adds scenario for IPv6 addresses

* Checks the way how  IPv6 addresses assigned to vNIC
* Eliminates hardcoded IPv4 subnet creation.
* Fixes problem with creating FIP for port with few addresses.
* Adds ping6 to remote_client

Partially implements: blueprint ipv6-api-testing-parity
Change-Id: I728edf0165ba47b6f8930f2fb3d08bd29cfbb317
Merge "Adds scenario for IPv6 addresses"