[systemd-devel] Add ARCH parameter to /etc/os-release

[Askar Safin]

> I was quite explicit about that when I initially designed multiarch. :-)
:)
Okey, okey, there is no primary arch :)
So, I think the arch which is the closest to be "primary arch" should go first.
Arch, which is the most suitable to be the arch in "setarch" command.
In some cases there is no such arch, but in the most popular cases we can pick some the most suitable arch.
I just want this to do the "setarch" trick or to do that "nspawn" trick.
It is useful to have some "default" arch.

For example, we can do the following in "nspawn":
1. If there is no any special option, it will read os-release and set (via trick similar to "setarch") arch which goes first in os-release
2. If there is some option (for example, --arch), it will set arch which is presented in this option. (Also, it may throw warning if there is no such arch in the os-release)