[thread-cert] Thread 1.2 CI with OTBR and Backbone link (#5489)

Thread 1.2 CI with OTBR and Backbone link:
- Run OTBR in Dockers with Backbone link
- Enhance node.py to work with OTBR Docker
- Add Packet Verification for 5.11.1
  - incomplete, some steps can not pass yet, just to make sure
    Backbone traffic verification works
- Support running multiple tests simultaneously (default: each test
  run 3 instances)
- Build OTBR Docker using OpenThread PR code
- Upload code coverage in Docker

Some implementation details:
- Most existing code of node.py is shared by OTBR Docker
- Backbone related test scripts are found in
  tests/scripts/thread-cert/backbone
- A new script tests/scripts/thread-cert/run_bbr_tests.py is added to
  manage multiple running tests
- Test configuration differs according to PORT_OFFSET
  - Backbone interface name: Backbone{PORT_OFFSET}
  - Backbone network prefix: 91{PORT_OFFSET:02x}::/64
  - Docker instance name: otbr_{PORT_OFFSET}_{nodeid}
  - Output Files:
    - Pcap:
      - Thread: {test_name}_{PORT_OFFSET}.pcap
      - Backbone: {test_name}_{PORT_OFFSET}_backbone.pcap
      - Merged: {test_name}_{PORT_OFFSET}_merged.pcap
    - Log: {test_name}_{PORT_OFFSET}.log

tests/scripts/thread-cert/pktverify/layer_fields.py

@@ -514,6 +514,7 @@ _LAYER_FIELDS = {
     'thread_nm.tlv.type': _list(_auto),
     'thread_nm.tlv.ml_eid': _ext_addr,
     'thread_nm.tlv.target_eid': _ipv6_addr,
+    'thread_nm.tlv.status': _auto,
     # thread_meshcop is not a real layer
     'thread_meshcop.len_size_mismatch': _str,
     'thread_meshcop.tlv.type': _list(_auto),