Adds option to reset stats on each collection.
Adds option to reset stats on each collection.

Zookeeper's bytes sent, bytes recieved, min/max/average latency
are maintained throughout an entire daemon's lifetime unless
you call `srst`. This means that the max latency stat ends up
being a high water mark rather than anything useful to graph.

sending reset_stats=True will reset the server stats after
each collection.

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