adb: fix test_device.FileOperationsTest.test_push_empty.

It was doing a test with `[ -d foo`, without the closing square bracket.

Test: python -m unittest test_device.FileOperationsTest.test_push_empty
Change-Id: I996b98850cf916986ef969768a7235547fcc404a
diff --git a/test_device.py b/test_device.py
index 9f45115..c3166ff 100755
--- a/test_device.py
+++ b/test_device.py
@@ -751,7 +751,7 @@
                 shutil.rmtree(host_dir)
 
     def test_push_empty(self):
-        """Push a directory containing an empty directory to the device."""
+        """Push an empty directory to the device."""
         self.device.shell(['rm', '-rf', self.DEVICE_TEMP_DIR])
         self.device.shell(['mkdir', self.DEVICE_TEMP_DIR])
 
@@ -767,9 +767,10 @@
 
             self.device.push(empty_dir_path, self.DEVICE_TEMP_DIR)
 
-            test_empty_cmd = ['[', '-d',
-                              os.path.join(self.DEVICE_TEMP_DIR, 'empty')]
+            remote_path = os.path.join(self.DEVICE_TEMP_DIR, "empty")
+            test_empty_cmd = ["[", "-d", remote_path, "]"]
             rc, _, _ = self.device.shell_nocheck(test_empty_cmd)
+
             self.assertEqual(rc, 0)
             self.device.shell(['rm', '-rf', self.DEVICE_TEMP_DIR])
         finally: