v0.2.1: various fixes from SCA development
- AgentContext: add accessor for last ping in ms
- BaseCmdAgent: make set_subagent_master compatible with call while terminating
- BaseCmdAgent: release subagents if terminate w/o cleanup by set master to top + rel. fixes
- CmdCoreAgent: in process_heartbeat, ensure top agent always followed
- EcsCoreAgent: in uninit to init trans, do not configure and error if no config tag
- Change default ports to the ones defined in previous prototype + doc