Ensures that messages are fully read before each append. Adds more
Zookeeper hits, but ensures logs won't be overwritten by multiple
daemons.
Also don't use a set on the client side, to avoid "removing duplicate"
entries erroneously.
We need to do a bit more finagling with the logger on termination to
ensure that all messages are written and the queue drained before
actually terminating.
Adds the ability to send node daemon logs to Zookeeper to facilitate a
command like "pvc node log", similar to "pvc vm log". Each node stores
its logs in a separate tree under "/logs" which can then be combined or
queried. By default, set by config, only 2000 lines are kept.
