bug#51442: Non-default umask when using guix system leads to wrong file permissions

[Josselin Poiret]

Hi,

As reported on IRC by wonko
(https://logs.guix.gnu.org/guix/2021-10-27.log#115445), when running
‘guix system’ under a different umask, some files are created with the
wrong permissions.  This can happen because ‘sudo’ does by default keeps
the umask it is running on (by ORing it with the default one, often
022).

I'm not sure what would be the best way to go about this, I suggest
checking if umask == #o022, and if not, print a warning and set it to
#o022, and only in ‘guix system’.

What do you think?

Best,
Josselin Poiret