In e328aa49 (component/nxdtest: Prepare for nxdtest!13 (merged)) I reworked how nxdtest script is generated and splitted it into nxdtest itself and .nxdtest.pyexe python interpreter, so that sys.executable could be used to correctly spawn other python scripts:

3) rework how nxdtest script is generated and split it into .nxdtest.pyexe and
   nxdtest itself. .nxdtest.pyexe is python interpreter via which nxdtest is run.
   This interpreter has all eggs required by nxdtest in sys.path, so that
   nxdtest could spawn its trun.py via sys.executable. If we don't care to have
   properly setup sys.executable, trun.py will fail when importing any module that
   nxdtest.py could already successfully import.

   Initially I tried to workaround this issue via adjusting $PYTHONPATH <-
   sys.path in main nxdtest script, but @jerome points out that, $PYTHONPATH,
   if set, also affects processes that trun.py spawns, which is not good:

   https://lab.nexedi.com/nexedi/slapos/merge_requests/1095#note_146799

   -> so fix this via running nxdtest via environment where sys.executable is
   properly setup python interpreter with path for all eggs that nxdtest has
   access to.

   Because we already have half-way workarounds for similar problem in several
   places, and because running a script with correctly setup sys.executable is
   generally better, I would say it should be a good idea to rework
   zc.recipe.egg:scripts to generate all scripts to work this way, but I do not
   want to fight about it.

   So let's leave this scheme nxdtest-specific for now.

This patch addresses the last paragraph and provides a general pyprog buildout macro that could be used to generate python script for any entry point to run with correctly set sys.executable.

/cc @jerome