alpine3.12 images only have linux/amd64

[ttshivers]

On Dockerhub, *-alpine3.12 only have linux/amd64 and no other architectures. It appears as if they should have more architectures:
https://github.com/nodejs/docker-node/blob/master/architectures
https://github.com/nodejs/docker-node/blob/master/12/architectures
https://github.com/nodejs/docker-node/blob/master/14/architectures

[nschonni]

@tianon could this be from an issue caused with the images not building correctly on the official-images extended CI?

[ttshivers]

It looks like the images are failing to build:
https://doi-janky.infosiftr.net/job/multiarch/job/i386/job/node/
https://doi-janky.infosiftr.net/job/multiarch/job/arm32v6/job/node/
https://doi-janky.infosiftr.net/job/multiarch/job/s390x/job/node/
https://doi-janky.infosiftr.net/job/multiarch/job/ppc64le/job/node/
https://doi-janky.infosiftr.net/job/multiarch/job/arm64v8/job/node/
https://doi-janky.infosiftr.net/job/multiarch/job/arm32v7/job/node/
https://doi-janky.infosiftr.net/job/multiarch/job/arm32v6/job/node/

It appears that they are failing because in alpine 3.12, the package "python" was removed and instead offer "python2" or "python3".

Made a PR fixing this: #1331