ovs-vsctl: Allow "get" commands to create @names also.

ovs-vsctl: Allow "get" commands to create @names also.

This is useful for adding records that refer to other records by UUID, e.g.
   ovs-vsctl \
     -- set bridge br0 mirrors=@m \
     -- --id=@eth0 get port eth0 \
     -- --id=@eth0 get port eth1 \
     -- --id=@m create mirror name=mymirror select-dst-port=@eth0 \
                              select-src-port=@eth0 output-port=@eth1