ACCUMULO-2213 Make writer recovery in the Tracer more robust.

    * Cleans up writer reseting in the TraceServer, avoids overly broad catching.
    * tones down log levels in TraceServer to WARN because trace information is transient and we retry everything.
ACCUMULO-2224 Make ZooSession more resiliant in the face of transient DNS issues.

* retries if host is not found, up to 2xZK timeout (same as other IOExceptions), rather than bailing on any host name problem.
* adds utility method for getting the max time the JVM will cache host failures
* add test for said method
ACCUMULO-2225 handle IllegalArgumentExceptions from Hadoop on host lookup failure.

Looks for cases where we treat IOExceptions out of Hadoop specially, then attempts to replicate for UnknownHostExceptions that have been wrapped in IllegalArgumentExceptions.