Merge branch 'ld/p4-test-py3' into HEAD

The test scripts for "git p4" (but not "git p4" implementation
itself) has been updated so that they would work even on a system
where the installed version of Python is python 3.

* ld/p4-test-py3:
  git-p4 tests: time_in_seconds should use $PYTHON_PATH
  git-p4 tests: work with python3 as well as python2
  git-p4 tests: cd to / before running python