Bootstrap not working, maybe allow forcing arch

[oanylund]

Hi,

Thanks for ubi!

When bootstrapping ubi on two different distributions of Linux I get:
boostrap-ubi.sh: Cannot determine what binary to download for your CPU architecture

uname -m returns armv7l on one and aarch64 on the other.
For reference this is on Raspberry Pi OS and Ubuntu Server (also running on a rpi)

Could it be good to have to allow forcing aarch when bootstrapping?

[autarch]

Adding support for more platforms shouldn't be too hard. I just need to get the uname -m and uname -s output from them. But I'd also be up for a PR that adds support for just using KERNEL and ARCH variables if they're set.

[autarch]

Actually, it occurs to me that maybe it'd better to just allow one env var that is the file name to download. That's probably simpler to use and document.

[oanylund]

I think that is a good option which will work nicely as a last resort and requires no maintenance from a developer pov. 👍

[autarch]

I updated the bootstrap script to try to handle more platforms and CPU architectures. It now also checks for a FILENAME argument which can be used to bypass platform detection entirely.