hosts/gentoo: recognize systemd for nfsd startup and
replace "service" command with /etc/init.d/nfs
Fixing so localhost hosts file entry is not lost when updating hostname. Addresses Issue #2383.
Merge pull request #2384 from nmische/ubuntu_hostname_fix

guests/ubuntu: Fixing so localhost hosts file entry is not lost when updating hostname....
Update CHANGELOG
Merge pull request #2382 from timgus/gentoo_systemd

hosts/gentoo: recognize systemd for nfsd startup and replace "service" command with /etc/init.d/nfs
Update CHANGELOG
hosts/gentoo: use subprocess machinery

/cc @timgus