ovs-ofctl: Use vconn_open() instead of vconn_open_block() in open_vconn__().

ovs-ofctl: Use vconn_open() instead of vconn_open_block() in open_vconn__().

All of the paths in open_vconn__(), except the one path that calls
vconn_open() directly, just start the connection and do not block until
it completes.  This changes the remaining path to work the same way.

This will be important in an upcoming commit when in some cases we need to
take an action between opening and connecting.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>