ACCUMULO-3421 Retry initialization of trace client

If we fail to connect to ZK for some reason,
we will never get the watcher set and tracing will
never be initialized properly. Add a simple retry
to ensure that it happens.
ACCUMULO-3424 Remove requirement for properties on provided token.
Merge branch '1.6'
ACCUMULO-3426 return this in setDurability
Merge branch 'master' of http://git-wip-us.apache.org/repos/asf/accumulo
ACCUMULO-3427 Switch LoggingRunnable from log4j to slf4j logger