Tests: Fix test bridge - add port after stopping controller on Windows

Tests: Fix test bridge - add port after stopping controller on Windows

On Windows the file which is used for the named pipe connection (`punix:file`)
is not deleted when the process is closed.

Try to delete the `controller` file and fail if we can't (on Windows you can't
delete a file if there still an opened handle to it).

Also add a check to see if the `ovs-testcontroller` was successfully started.

Signed-off-by: Alin Gabriel Serdean <aserdean@ovn.org>
Acked-by: Sairam Venugopal <vsairam@vmware.com>