ARROW-11717: [Integration] Fix intermittent flight integration failures with rust

[alamb]

Background

Thanks to the 🦅 👁️ of @lidavidm #9583 (comment) it appears that the Rust flight integration test prints "Server listening" before the server is actually read to accept connections. Thus creating a race condition: if the tests try and start faster than the rust server can actually be setup then we see integration test failures as shown in https://issues.apache.org/jira/browse/ARROW-11717:

Traceback (most recent call last):
  File "/arrow/dev/archery/archery/integration/runner.py", line 308, in _run_flight_test_case
    consumer.flight_request(port, **client_args)
  File "/arrow/dev/archery/archery/integration/tester_cpp.py", line 116, in flight_request
    run_cmd(cmd)
  File "/arrow/dev/archery/archery/integration/util.py", line 148, in run_cmd
    raise RuntimeError(sio.getvalue())
RuntimeError: Command failed: /build/cpp/debug/flight-test-integration-client -host localhost -port=33569 -scenario auth:basic_proto
With output:
--------------
-- Arrow Fatal Error --
Invalid: Expected UNAUTHENTICATED but got Unavailable

Changes

This PR changes the Rust flight scenario harnesses to print the ready message after the server is actually ready.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-11717

[lidavidm]

@alamb if I'm not mistaken, serve().await? will block until the server is terminated, which means that the test is now stuck. Is there any way to start a server without waiting for it? (Most other gRPC implementations provide this.)

Alternatively, we could add a retry loop…

[alamb]

@lidavidm good call -- let me try something else

[alamb]

@lidavidm thank you for the help -- it is like you are writing the code for me :)

[alamb]

The integration test passed: https://github.com/apache/arrow/pull/9593/checks?check_run_id=1995394206

I'll manually retrigger a few times to see if there might be still something lurking

[lidavidm]

LGTM. Thanks for fixing this!

[alamb]

Thanks @alamb !