[doc] agent upgrade protocol definition
[minor] clean up unused source file
[minor] Add `-V` flag to agent to return current version
[minor] Add PID to registration format
[medium] Upgrade module
[minor] gofmt
[medium] AgentDestroy module: kills an agent and deletes its binary
[major] Scheduler logic to control upgrade and cleanup of agents
[minor] update Makefile for RPM and DEB generation