bpo-18174: Fix file descriptor leaks in tests (GH-7408)

* test_tempfile.test_no_leak_fd() mocks os.close() but it doesn't
  call the original os.close() method and so leaks an open file
  descriptor. Fix the test by calling the original os.close()
  function.
* test_posix.test_fdopen_directory(): close the directory file
  descriptor when the test completes.

Lib/test/test_posix.py

@@ -199,6 +199,7 @@ class PosixTester(unittest.TestCase):
     def test_fdopen_directory(self):
         try:
             fd = os.open('.', os.O_RDONLY)
+            self.addCleanup(os.close, fd)
         except OSError as e:
             self.assertEqual(e.errno, errno.EACCES)
             self.skipTest("system cannot open directories")

Lib/test/test_tempfile.py

@@ -821,6 +821,7 @@ class test_NamedTemporaryFile(TC):
         old_fdopen = os.fdopen
         closed = []
         def close(fd):
+            old_close(fd)
             closed.append(fd)
         def fdopen(*args):
             raise ValueError()