Added an extra log statement to the DFSOutputStream
Added log statement to indicate that we're forcing a namenode block
update
Added some instrumentation of some of the main locks used on the
namenode.
Removed some annoying unnecessary RPC log messages, and added a 'name'
tag to name the spans in the rpc invoker.
Changed the startTrace logpoints in DataXceiver to just logEvents. 
Starting traces here isn't such a good idea; background tasks end up
accidentally starting traces when really we're not interestedin them.
Use XTraceResourceTracing branching API to log the explicit computation
boundaries when kicking off new threads.  Also, add some names when
setting XTraceContext to give spans names.