Do not consider missing command as internal failure.

client/tests/run_isolated_smoke_test.py

Index: client/tests/run_isolated_smoke_test.py
diff --git a/client/tests/run_isolated_smoke_test.py b/client/tests/run_isolated_smoke_test.py
index c96f010b7cdccb63782f33cf83e1923518bffebf..da06c889e138c0d36dcc5ee9b06bc7a83ee008a1 100755
--- a/client/tests/run_isolated_smoke_test.py
+++ b/client/tests/run_isolated_smoke_test.py
@@ -295,7 +295,10 @@ class RunIsolatedTest(unittest.TestCase):
     expected = ['state.json', isolated_hash]
     out, err, returncode = self._run(self._cmd_args(isolated_hash))
     self.assertEqual('', out)
-    self.assertIn('No command to run\n', err)
+    self.assertIn(
+        '<The .isolated doesn\'t declare any command to run!>\n'
+        '<Check your .isolate for missing \'command\' variable>\n',
+        err)
     self.assertEqual(1, returncode)
     actual = list_files_tree(self.cache)
     self.assertEqual(sorted(expected), actual)