agent: use harpoon-supervisor
delete harpoon-container
agent: remove unused types from lib
agent: kill running containers on recovery

This preserves the previous agent behavior when using harpoon-container.
agent: restore instrumentation in supervisor
agent: supervisor connect handles ECONNREFUSED
agent: clarify terminal state handling
agent: clean up supervisor test
agent: reuse eventsource encoder in supervisor
Merge pull request #55 from soundcloud/harpoon-agent-supervisor

agent: use harpoon-supervisor