[sosreport] do not pass chunksize to ThreadPoolExecutor.map()

3.4 python also appears to be broken by an unnecessary use of the
chunksize argument when threading plugins landed.  According to
the docs it defaults to 1, and has no effect for the
ThreadPoolExecutor class:

  "For very long iterables, using a large value for chunksize can
   significantly improve performance compared to the default size
   of 1. With ThreadPoolExecutor, chunksize has no effect."

Related: #1603

Signed-off-by: Bryan Quigley <[email protected]>
Signed-off-by: Bryn M. Reeves <[email protected]>

sos/sosreport.py

@@ -973,7 +973,7 @@ def collect(self):
             self.plugpool = ThreadPoolExecutor(self.opts.threads)
             # Pass the plugpool its own private copy of self.pluglist
             results = self.plugpool.map(self._collect_plugin,
-                                        list(self.pluglist), chunksize=1)
+                                        list(self.pluglist))
             self.plugpool.shutdown(wait=True)
             for res in results:
                 if not res: