pep8 fixes (semi-automatic)
added feature for KWS benchmark; fix xranges error

* there was an error in original code: xranges can not be just added. use itertools.chain instead
* support benchmarking of KWS, including:
  - https support
  - text/html responses which do not return elapsed time (use local timer)
das_bench improvements

* added options: minclients, repeat
* writelock when writing execution time to prevent race condition in multiprocessing
* support other output formats than pdf, such as png
minor cleanup
Merge pull request #4052 from dmwm/kwd-search-benchmark-good

Benchmark tool improvements