Use local copy of python distro to include a subdir

[earlephilhower]

fix #5792

[mcspr]

@earlephilhower i think .zip needs to be repacked again, zfile.namelist()[0] picks file instead of dir name:

$ cat test.py
import sys
import zipfile
zfile = zipfile.ZipFile(sys.argv[1])
print(zfile.namelist()[0])

$ python test.py dist/python-3.7.2.post1-embed-win32.zip
python-3.7.2.post1/_asyncio.pyd

#5635 (comment) being latest mention of this