Exceptions other than OSError are not surfaced.
This caused errors like this to be printed, but not block presubmit,
allowing bugs to sneak in.

Exception in thread Thread-8:
Traceback (most recent call last):
  File "C:\b\s\w\ir\cipd_bin_packages\cpython\bin\Lib\threading.py", line 801, in __bootstrap_inner
    self.run()
  File "C:\b\s\w\ir\cipd_bin_packages\cpython\bin\Lib\threading.py", line 754, in run
    self.__target(*self.__args, **self.__kwargs)
  File "C:\b\s\w\ir\kitchen-checkout\depot_tools\presubmit_support.py", line 199, in _WorkerFn
    result = self.CallCommand(test)
  File "C:\b\s\w\ir\kitchen-checkout\depot_tools\presubmit_support.py", line 170, in CallCommand
    p = subprocess.Popen(cmd, **test.kwargs)
  File "C:\b\s\w\ir\kitchen-checkout\depot_tools\subprocess2.py", line 143, in __init__
    super(Popen, self).__init__(args, **kwargs)
  File "C:\b\s\w\ir\cipd_bin_packages\cpython\bin\Lib\subprocess.py", line 390, in __init__
    errread, errwrite)
  File "C:\b\s\w\ir\cipd_bin_packages\cpython\bin\Lib\subprocess.py", line 640, in _execute_child
    startupinfo)
TypeError: environment can only contain strings

https://logs.chromium.org/logs/infra/buildbucket/cr-buildbucket.appspot.com/8898840708364523888/+/steps/presubmit/0/stdout

Change-Id: I34e65d8c0050eed7ed26fd782e0a5dc8616f30f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1877051
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>