remove unnecessary gce serviceaccounts assertion

Author: zshihang

apitools/base/py/credentials_lib.py

@@ -337,10 +337,6 @@ def _ScopesFromMetadataServer(self, scopes):
         if not util.DetectGce():
             raise exceptions.ResourceUnavailableError(
                 'GCE credentials requested outside a GCE instance')
-        if not self.GetServiceAccount(self.__service_account_name):
-            raise exceptions.ResourceUnavailableError(
-                'GCE credentials requested but service account '
-                '%s does not exist.' % self.__service_account_name)
         if scopes:
             scope_ls = util.NormalizeScopes(scopes)
             instance_scopes = self.GetInstanceScopes()

apitools/base/py/credentials_lib_test.py

@@ -69,7 +69,7 @@ def _GetServiceCreds(self, service_account_name=None, scopes=None):
                 credentials = self._RunGceAssertionCredentials(
                     service_account_name=service_account_name,
                     scopes=scopes)
-            self.assertEqual(3, opener_mock.call_count)
+            self.assertEqual(2, opener_mock.call_count)
         return credentials
 
     def testGceServiceAccounts(self):