Zookeeper should not warn about "An exception was thrown while closing send thread"

In commit https://github.com/apache/zookeeper/commit/11c07921c15e2fb7692375327b53f26a583b77ca the message printed when closing a connection to Zookeeper was changed from being logged as a debug message to a warning message.  The comment next to the message confirms that this is "expected" and therefore, it seems unjustified to use a warning level. 

Can we tune this down back to debug (or info) level? I would not mind submitting a pull request if there is consensus.

The full error we are seeing is the following:

An exception was thrown while closing send thread for session 0x1067b8748f00775.

with stack strace:

EndOfStreamException: Unable to read additional data from server sessionid 0x1067b8748f00775, likely server has closed socket at org.apache.zookeeper.ClientCnxnSocketNIO.doIO(ClientCnxnSocketNIO.java:77) at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:350) at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1280)