Implemented a TracingAgent base class. Bug: 267675642 Test: manually tested. python3 tracing_agent.py --guest_serial 10.42.0.235 --host_ip 10.42.0.235 --host_tracing_file_name qnx_trace --out_dir test_trace --duration 50 --host_username root Change-Id: I6ea3b314fc920b47c734dcc7860937276d33e87e