Refactored the 'os security group show' command to use the SDK
when neutron is enabled, but continue to use the nova client
when nova network is enabled.
Added a release note for the change in security group rules output
due to Network v2. The column names remain unchanged to maintain
backwards compatibility.
Change-Id: I25233ddb8115d18b8b88affb3de13346084a339d
Partial-Bug: #1519511
Implements: blueprint neutron-client
