This includes two logically separate changes:
- on the host, try not to require sudo when running the build scripts
- namely when interacting with the docker daemon, this requires
the unix user on the host to be part of the `docker` group
- this solves part of https://github.com/spesmilo/electrum/issues/7602
- while running inside the docker containers, do not run as root
- this means that e.g. files created in mounted folders should
no longer be owned by root on the host
- there is some code duplication involved here - not sure
how it could be deduped.
Had to also bump ubuntu version 18.04->20.04,
as was getting errors running the self-compiled pyinstaller otherwise (weird...):
```
from .utils.git import get_repo_revision
ModuleNotFoundError: No module named 'PyInstaller.utils'
```
(similar to https://github.com/pyinstaller/pyinstaller/issues/4403 )
-----
Note re appimage: when trying to compile python 3.8.x on ubuntu 16.04, I am getting:
./Modules/posixmodule.c: In function ‘os_copy_file_range_impl’:
./Modules/posixmodule.c:10351:15: error: implicit declaration of function ‘copy_file_range’ [-Werror=implicit-function-declaration]
ret = copy_file_range(src, p_offset_src, dst, p_offset_dst, count, flags);
This is because ubuntu 16.04 has too old glibc.