This solves the race condition that leaves stdout as a StringIO when
this is executed twice in parrallel ( #20180928-1D89375 )

But this prints
  No config file found, using default configuration
on sys.stderr at every execution, but that's acceptable.

Once we update pylint, we can disable this warning by setting
verbose=false ( this is not yet available on pylint 1.4.4 )

/reviewed-on nexedi/erp5!758