Disable failing CPython test under Cinder

Summary:
`test_executable_without_cwd` is failing in `test_subprocess`. It wants to do a subprocess.Popen(['bogus', ...], executable=...) and make sure CPython can find the right path.

In our psuedo-builds this doesn't seem to work, so this disables it under Cinder.

Reviewed By: jbower-fb

Differential Revision: D64726775

fbshipit-source-id: 7c6328f1bc00fd9d847cb00cf94de3e4c2211965

Lib/test/test_subprocess.py

@@ -494,6 +494,8 @@ def test_executable_with_cwd(self):
                      'Test is not venv-compatible')
     @unittest.skipIf(sysconfig.is_python_build(),
                      "need an installed Python. See #7774")
+    @unittest.skipIf(getattr(sys.implementation, '_is_cinder', False),
+                     "Cinder tests aren't installed Python")
     def test_executable_without_cwd(self):
         # For a normal installation, it should work without 'cwd'
         # argument.  For test runs in the build directory, see #7774.