[PATCH 1 of 8 py3] dispatch: consolidate formatting of arguments

[Augie Fackler]

On Tue, Mar 21, 2017 at 10:11 PM, Kevin Bullock
<kbullock+mercurial at ringworld.org> wrote:
>     $ PYTHON3=/path/to/python3 python run-tests.py test-check-py3-commands.t


Should be `python run-tests.py
--with-python3=/absolute/path/to/python3 test-check-py3-commands.t`.