Description of problem:

Updating systemd package add myhostname to the hosts line of /etc/nsswith.conf by postinstall scriptlet.
I think this script should run only time to install, not run time to upgrade.

Version-Release number of selected component (if applicable):

systemd-219-26.el7.x86_64

How reproducible:

Updating systemd package

Steps to Reproduce:
1. grep '^hosts:' /etc/nsswitch.conf
hosts:      files dns

2. yum update systemd

Actual results:
# grep '^hosts:' /etc/nsswitch.conf
hosts:      files dns myhostname

Expected results:
# grep '^hosts:' /etc/nsswitch.conf
hosts:      files dns

Additional info:

Some users would not like to use nss-myhostname.
These users delete myhostname from the hosts line of /etc/nsswith.conf.
Updating systemd package break this settings.

See also:
Why 'getent' command is resolving ipv6 address only and not ipv4 in Red Hat Enterprise Linux 7 ?
https://access.redhat.com/solutions/1287253