Use StatefulConnection class to verify connectivity in SG tests

There are two security group tests that are running for more than
20 minutes with RHEL image:
 - test_multiple_ports_portrange_remote
 - test_overlapping_sec_grp_rules
It happens because of the lack of privileges. I think it makes
sense to utilize the existing StatefulConnection class as it
has better service handling (start/stop) with all necessary
permissions

Change-Id: Iaca6fd3e6ed3c64ab3ca22817ad461479ecfa189
2 files changed