And it looks like pykwalify dependency
is causing random fails during CI pipelines.

* Tavern test dir path added as a parameter to enable running tests from other locations than default api test dir.
* Renamed original python benchmark tester to avoid confusion which script to run.

Set python3 as default interpreter for tox env. Fixes issue when there are more than one interpreter installed.

* Usage of pytest-benchmarks is dropped since it call tests
  sequentially which very long time to complete, instead original
  tavern tests are used
* Time measuring is done via durations switch to pytest and tavern
* During benchmarking validate_response.py is disabled using nevly
  introduced env variable
* Each run creates xml junit file with time data
* After all runs data from files are combined and report file is
  generated
* Tests above threshold are marked with red

* New script for running benchmarks
* Benchmarks are now runned several times to cheat caching
* Data from each run is combined together

- Added pytest-xdist plugin to enable multithreaded support for tests
- Added durations option to measure test execution time

- removed tests_require from setup.py it is depreciated in favor of tox
- setup test env in tox
- removed gitpython dependency