clean up hostname service script
clean up hostname service script

- use _ throw-away variable to get rid of a shellcheck warning
- remove tests for /etc/hostname and just try to read it
- drop reference to bash HOSTNAME variable.
- make source of host name more accurate

X-Gentoo-Bug: 850577
X-Gentoo-Bug-URL: https://bugs.gentoo.org/850577

OpenRC/openrc,OpenRC/openrc,OpenRC/openrc