Add Python-3.8.0b1

[fikisipi]

It would make sense to add the beta before the release lands, so that package maintainers have time to adjust their pipelines and build wheels for 3.8.

[njsmith]

The problem is, building wheels for 3.8b1 isn't very useful if those wheels crash when you use them on 3.8-final :-)

@ambv When does the 3.8 ABI get frozen so people can start building wheels?

[auvipy]

after beta 3

[lkollar]

We could create an image with beta or experimental tag for folks who want to experiment with the new release until it stabilises. Otherwise I agree that we should wait until the ABI becomes stable to avoid ABI-incompatible wheels in the wild.

[njsmith]

The ideal for experimentation would be if we could arrange for pre-release wheels to get some unique tag, like cp38b1 or something. This would require some assistance from pip though to make these wheels installable...

[fikisipi]

It seems that b1 isn't even a part of https://www.python.org/static/files/pubkeys.txt so this won't work even if the ABI gets stable.

Maybe create another docker image for betas and skip gpg verify?