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ARROW-17785: [Java] Suppress flakiness from gRPC in JDBC driver tests (#14210)

I couldn't reproduce it, so I added a suppression instead. 

In both cases, the error is that the server is uncontactable. That shouldn't happen, but I changed the tests to also bind to port 0 instead of using a potentially flaky free port finder.

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>