ci: Print output in case of compile error

[dkwingsmt]

Description

This PR prints the CalledProcessError.output before the error is thrown and crashes the app. This happens when the test fails to compile. Without it, you only get the following message and will never know where to fix without running the command locally.

Command run successfully in 0.24 seconds: /opt/s/w/ir/cache/builder/src/out/host_debug_unopt/flutter_tester --disable-observatory --use-test-fonts /opt/s/w/ir/cache/builder/src/out/paragraph_test.dart.kernel.dill
Testing dart file /opt/s/w/ir/cache/builder/src/flutter/testing/dart/window_hooks_integration_test.dart
Generating snapshot for test /opt/s/w/ir/cache/builder/src/flutter/testing/dart/window_hooks_integration_test.dart
Traceback (most recent call last):
  File "/opt/s/w/ir/cache/builder/src/flutter/testing/run_tests.py", line 510, in <module>
    sys.exit(main())
  File "/opt/s/w/ir/cache/builder/src/flutter/testing/run_tests.py", line 485, in main
    RunDartTests(build_dir, dart_filter, args.verbose_dart_snapshot)
  File "/opt/s/w/ir/cache/builder/src/flutter/testing/run_tests.py", line 418, in RunDartTests
    RunDartTest(build_dir, dart_test_file, verbose_dart_snapshot, True)
  File "/opt/s/w/ir/cache/builder/src/flutter/testing/run_tests.py", line 225, in RunDartTest
    SnapshotTest(build_dir, dart_file, kernel_file_output, verbose_dart_snapshot)
  File "/opt/s/w/ir/cache/builder/src/flutter/testing/run_tests.py", line 217, in SnapshotTest
    subprocess.check_output(snapshot_command, cwd=buildroot_dir)
  File "/opt/s/w/ir/cipd_bin_packages/cpython/lib/python2.7/subprocess.py", line 223, in check_output
    raise CalledProcessError(retcode, cmd, output=output)
subprocess.CalledProcessError: Command '['/opt/s/w/ir/cache/builder/src/out/host_debug_unopt/dart-sdk/bin/dart', '/opt/s/w/ir/cache/builder/src/out/host_debug_unopt/gen/frontend_server.dart.snapshot', '--enable-experiment=non-nullable', '--no-sound-null-safety', '--sdk-root', '/opt/s/w/ir/cache/builder/src/out/host_debug_unopt/flutter_patched_sdk', '--incremental', '--target=flutter', '--packages', '/opt/s/w/ir/cache/builder/src/flutter/testing/dart/.packages', '--output-dill', '/opt/s/w/ir/cache/builder/src/out/window_hooks_integration_test.dart.kernel.dill', '/opt/s/w/ir/cache/builder/src/flutter/testing/dart/window_hooks_integration_test.dart']' returned non-zero exit status 254

(See https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket.appspot.com/8858721042103931248/+/steps/Host_Tests_for_host_debug_unopt/0/stdout?format=raw)

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[chinmaygarde]

I think the presubmit failure is a known flake that has been fixed. I have re-run it but I can't recall if it required a rebase as well. If the CQ fails after the test run still, please rebase and land. Thanks.

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

• The status or check suite build_and_test_linux_unopt_debug has failed. Please fix the issues identified (or deflake) before re-applying this label.