Support accepting and displaying port names in OVS tools.

Support accepting and displaying port names in OVS tools.

Until now, most ovs-ofctl commands have not accepted names for ports, only
numbers, and have not been able to display port names either.  It's a lot
easier for users if they can use and see meaningful names instead of
arbitrary numbers.  This commit adds that support.

For backward compatibility, only interactive ovs-ofctl commands by default
display port names; to display them in scripts, use the new --names
option.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Tested-by: Aaron Conole <aconole@redhat.com>