D2988: fix: use a portable python script instead of sed in test

[durin42 (Augie Fackler)]

durin42 accepted this revision.
durin42 added a comment.
This revision is now accepted and ready to land.


  Sorry, this fell through the cracks somehow. Queued.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D2988

To: hooper, #hg-reviewers, durin42
Cc: durin42, mharbison72, mercurial-devel