[tests] add test case Cert_9_2_02 (#3589)

1. Add new test case **Cert_9_2_02**. Since the test case contains 2
topologies, added 2 new files:
- `Cert_9_2_02A_MGMTCommissionerSet.py`,
- `Cert_9_2_02B_MGMTCommissionerSet.py`.

2. Add mesh_cop tlvs parsing. The corresponding file is
`mesh_cop.py`. The mesh_cop tlvs are used in many cases. For example,
`CommissionerSessionId` is used in both the parsing of **Commissioning
Data**(in mle) and the parsing of **CoAP**. Collected all mesh_cop
tlvs refered in Thread into this file with some unused tlvs
unimplemented.

3. Reuse `SubTlvsFactory` in `network_data.py`. `SubTlvsFactory` are
used to choose the corresponding factory of specific tlv and do the
parsing of it. The `NetworkLayerTlvsFactory` in `network_layer.py` had
exactly the same function with it (almost the same code). Moved the
`SubTlvsFactory` into a new file `tlvs_parsing.py` and change the
usage in `network_data.py` and `network_layer.py`. This helps us
remove some redundant code.

4. Some format issues. Remove some trailing spaces.

tests/scripts/thread-cert/test_network_layer.py

@@ -481,24 +481,5 @@ class TestThreadNetworkDataFactory(unittest.TestCase):
         self.assertEqual(tlvs, thread_network_data.tlvs)
 
 
-class TestNetworkLayerTlvsFactory(unittest.TestCase):
-
-    def test_should_create_tlv_when_parse_method_is_called(self):
-        # GIVEN
-        class DummyNetworkDataTlvsFactory:
-
-            def parse(self, data, message_info):
-                return bytearray(data.read())
-
-        tlv = any_tlv_data()
-
-        factory = network_layer.NetworkLayerTlvsFactory({tlv[0]: DummyNetworkDataTlvsFactory()})
-
-        # WHEN
-        actual_tlvs = factory.parse(io.BytesIO(tlv), None)
-
-        # THEN
-        self.assertEqual(tlv[2:], actual_tlvs[0])
-
 if __name__ == "__main__":
     unittest.main()