Revert "[devicelab] Do not wait for connections after process has exited"

[jonahwilliams]

Reverts #54497

This change has led to a new flake:

01:08 +37 -1: test\run_test.dart: run.dart script exits with code 1 when fails to connect [E]                                                                                                          
  Expected: not <0>
    Actual: <0>
  [ stderr from test process ]
  
  
  
  [ end of stderr ]
  
  [ stdout from test process ]
  
  
  
  ��������������╡ ••• Running task "smoke_test_setup_failure" ••• ╞���������������
  
  
  Executing: C:\b\s\w\ir\k\flutter\bin\cache\dart-sdk\bin\dart --enable-vm-service=0 --no-pause-isolates-on-exit bin/tasks/smoke_test_setup_failure.dart in C:\b\s\w\ir\k\flutter\dev\devicelab
  [smoke_test_setup_failure] [STDOUT] Observatory listening on http://127.0.0.1:58612/1bRsp3TbNHI=/
  "C:\b\s\w\ir\k\flutter\bin\cache\dart-sdk\bin\dart" exit code: 0
  
  
  [ end of stdout ]
  
  package:test_api         expect
  test\run_test.dart 29:7  main.<fn>.expectScriptResult
  

01:08 +37 -1: test\run_test.dart: run.dart script exits with code 1 when results are mixed     

[yjbanov]

Darn. The flake was exactly what I was aiming to fix.

[yjbanov]

@jonahwilliams where did you see it fail? Cirrus? LUCI?

[jonahwilliams]

Landing on red since this is a revert