Peer server will be started and stopped repeatedly in the design.
This step ensures its stop doesn't affect the next start.
The patch includes goroutine stop and timer trigger remove.
Use PUT /_state?prevExist=true in the protocol instead of PUT
/_state?prevValue=init. This lets people point one vanilla etcd at the
key prefix of another vanilla etcd and have it just work.
This is an initial version of the bootstrap code that seems to work
under the normal circumstances. I need to mock out a server that will
test out all of the error cases now.
