setup-hostname: no support for setting up the domain

setup-hostname only supports setting the sort hostname, but not a domain. The hostname is written to /etc/hostname. setup-alpine, however, expects hostname -f (which gets the information from /etc/hostname) to contain a domain part and defaults to my.domain if none is found.

The result is that there does not seem to be a straightforward way of having correct network setup after running setup-alpine. One always ends up with <hostname>.my.domain in /etc/hosts and manually editing two files is required to fix the setup.