Java client logs NPE if a connection is closed by client during negotiation

This is noted in KUDU-1894 but I don't know if it's the root cause of the ITClient flakiness, so I'm opening a new JIRA for this:

If the client is closed (or a connection to a TS is closed) while it's in the progress of negotiating, it will result in an error stating "javax.net.ssl.SSLException: renegotiation attempted by peer; closing the connection" followed by an NPE in sendQueuedRpcs().

This is being triggered by Impala in a stress workload with a high query rate.