tests: Fix timing dependency bridge - multiple bridges share a controller

tests: Fix timing dependency bridge - multiple bridges share a controller

Without the fix, this test currently consistently fail when running
on Travis CI. Connecting to the controller can take more time than
running locally. Because the exact connecting time is variable, the
exact output should not be used for correctness checking.

Fixes: 85c55772a453(bridge: Fix controller status update)
Signed-off-by: Andy Zhou <azhou@ovn.org>
Acked-by: Joe Stringer <joe@ovn.org>