Added test for reattached security groups

We had a bug for OSP13 with openvswitch firewall driver that the established
connection can't be resumed after the security group has been removed from
the port and than added back. Need to test this behavior.

In order to keep the connection open there is a new StatefulConnection
class

Related-Bug: #1915530
Change-Id: I3c2f037180b35dbbd254d8b4ce69852d31391a9a
3 files changed