[PATCH 2 of 2] tests: replace yet more calls to `python` with $PYTHON

[Augie Fackler]

> On Jun 29, 2017, at 10:07 PM, Jun Wu <quark at fb.com> wrote:
> 
> Excerpts from Augie Fackler's message of 2017-06-29 16:18:57 -0400:
>>> On Jun 29, 2017, at 16:17, Augie Fackler <raf at durin42.com> wrote:
>>> 
>>> # HG changeset patch
>>> # User Augie Fackler <augie at google.com>
>>> # Date 1497993027 14400
>>> #      Tue Jun 20 17:10:27 2017 -0400
>>> # Node ID 298f967da627a90149e823cf9ae11fc503029d9f
>>> # Parent  8238b8e8920aee16caa57b97aef8bc988559c67b
>>> tests: replace yet more calls to `python` with $PYTHON
>>> 
>>> Summary: These are some simple cases. More to come in a future change.
>>> 
>>> Reviewers: krbullock
>>> 
>>> Differential Revision: https://hg-phab.durin42.com/D4 
>> 
>> I've mailed these patches here, but they're also in the experimental
>> phabricator we've set up. I figured I'd use these patches (and some
>> subsequent ones I've got) as test candidates since they're the exact kind
>> of change that's a ton easier in phabricator.
>> 
>> (We'll make a bigger email about phabricator with details on the
>> experiment once we get the kinks worked out.)
> 
> The patches look straightforward to me.
> 
> On Phabricator, I guess we need an "hg email" like tool to send patches to
> Phabricator. The default "arc diff" behavior does not fit our use-case.
> Since I'm a bit familiar with Phabricator, I can write one in contrib/.

Yeah.

We also need a way to land patches out of phabricator, which I think might take some doing.