build: Use sys.executable for Python path
build: Use sys.executable for Python path

When building the templates, it's assumed that `python` lives at
`python`. This is not always true, so using
[sys.executable](https://docs.python.org/3/library/sys.html#sys.executable)
will resolve the path correctly.

Signed-off-by: Rob Loach <4c58b37a60edcb7f0c248e9ae9d561bcb065f992@gmail.com>
Reviewed-by: Cyril Hrubis <b1e90efd3b808b8e0bcf2a9a55fd8b9a779bfd81@ucw.cz>

gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim