Get rid of ind_ovs_version

Reviewer: @poolakiran

With these changes the core of IVS is fully OpenFlow wire version independent, removing the need to configure a specific version.

The earlier forwarding pipeline changes allowed us to select the OpenFlow 1.0 or 1.3 forwarding models independent of the connected controllers' versions. For backwards compatibility, the --openflow-version command line option becomes a fallback for choosing the pipeline.