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.
Irving-cl