Cleanup node directory on clean shutdown

Cleanup etcd integration test helpers too
Don't export so much from EtcdCoordinator
Update coordinator to all Init to fail; refresh node dir ttl
Fix misleading log line.
Add a sanity check for node ttl
Use default etcd ports in koalemos
Locks are hard.
Merge pull request #62 from lytics/61-cleanup-node-key

Refresh node dir while running and cleanup on exit