RFE: Support setting hostname, locale and timezone

[dteleguin]

At the moment, generated image ends up with the following settings:

• hostname: localhost
  This comes from /etc/hostname which belongs to systemd RPM and contains "localhost" (however may be specific to my distro, Mageia). If the image is used as a systemd-nspawn bootable container, this static hostname prevents the transient hostname (= machine name) to be set correctly (as of systemd-230). Hence, the hostname may need to be set for VMs and to be unset for containers;
• locale: (not set)
• timezone: inherited from the build machine (?)

It would be nice to have an ability to configure this all on the image building stage. However, this can be tricky, since hostnamectl/localectl/timedatectl all require running systemd inside the image.

[dteleguin]

Of course this could be solved by manipulating /etc/hostname, /etc/locale.conf and /etc/localtime from a mkosi.postinst script, or even installing a first-run script into the image itself. Feel free to close if insignificant/irrelevant.

[dteleguin]

I have just noticed #105, so the hostname part seems to be dealt with already. I think setting timezone and locale could be implemented in a similar manner.

[poettering]

I'd probably add explicit support for setting the hostname, but I am not sure about /etc/locale.conf, as mkosi.extra/ appears fully sufficient to cover that, and similar for /etc/localtime.

@dteleguin would mkosi.extra/ suffice for you? If yes, we can close this and leave #105 for the hostname thing.

[dteleguin]

@poettering yep I'm OK with that, closing the issue