[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/network_layer.py

@@ -314,22 +314,3 @@ class ThreadNetworkDataFactory(object):
         tlvs = self._network_data_tlvs_factory.parse(data, message_info)
         return ThreadNetworkData(tlvs)
 
-
-class NetworkLayerTlvsFactory(object):
-
-    def __init__(self, tlvs_factories):
-        self._tlvs_factories = tlvs_factories
-
-    def parse(self, data, message_info):
-        tlvs = []
-
-        while data.tell() < len(data.getvalue()):
-            _type = ord(data.read(1))
-            length = ord(data.read(1))
-
-            factory = self._tlvs_factories[_type]
-            tlv = factory.parse(io.BytesIO(data.read(length)), message_info)
-
-            tlvs.append(tlv)
-
-        return tlvs