Quit bot process when we can't contact metadata server.

[jonathanmetzman]

Nothing can be done in the process so quit and try again.

Tries to fix:

 "AuthMetadataPluginCallback "<google.auth.transport.grpc.AuthMetadataPlugin object at 0x000001D8BDC56108>" raised exception!
Traceback (most recent call last):
  File "c:\clusterfuzz\src\third_party\google\auth\compute_engine\credentials.py", line 111, in refresh
    self._retrieve_info(request)
  File "c:\clusterfuzz\src\third_party\google\auth\compute_engine\credentials.py", line 88, in _retrieve_info
    request, service_account=self._service_account_email
  File "c:\clusterfuzz\src\third_party\google\auth\compute_engine\_metadata.py", line 234, in get_service_account_info
    return get(request, path, params={"recursive": "true"})
  File "c:\clusterfuzz\src\third_party\google\auth\compute_engine\_metadata.py", line 165, in get
    "metadata service. Compute Engine Metadata server unavailable".format(url)
google.auth.exceptions.TransportError: Failed to retrieve http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/[email protected]/?recursive=true from the Google Compute Enginemetadata service. Compute Engine Metadata server unavailable

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "c:\clusterfuzz\src\third_party\grpc\_plugin_wrapping.py", line 78, in __call__
    context, _AuthMetadataPluginCallback(callback_state, callback))
  File "c:\clusterfuzz\src\third_party\google\auth\transport\grpc.py", line 104, in __call__
    callback(self._get_authorization_headers(context), None)
  File "c:\clusterfuzz\src\third_party\google\auth\transport\grpc.py", line 91, in _get_authorization_headers
    self._request, context.method_name, context.service_url, headers
  File "c:\clusterfuzz\src\third_party\google\auth\credentials.py", line 133, in before_request
    self.refresh(request)
  File "c:\clusterfuzz\src\third_party\google\auth\compute_engine\credentials.py", line 117, in refresh
    six.raise_from(new_exc, caught_exc)
  File "<string>", line 3, in raise_from
google.auth.exceptions.RefreshError: Failed to retrieve http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/[email protected]/?recursive=true from the Google Compute Enginemetadata service. Compute Engine Metadata server unavailable
"

[oliverchang]

Is this not already caught by the existing catchall on line 167? the resulting behaviour seems like it would be the same?