Add scriptlet to enable nss-resolve

The default line is
> hosts: files dns myhostname
Some people might insert mymachines, most likely as:
> hosts: mymachines files dns myhostname
The scriptlet for nss-mdns inserts mdns before dns:
> hosts: ... files mdns4_minimal [NOTFOUND=return] dns ...

The scriptlet replaces 'files dns myhostname' with
> resolve [!UNAVAIL=return] myhostname files dns
This follows the upstream recommendation. myhostname is ordered earlier
because
a) it's more trustworthy than files or especially dns
b) resolve synthetizes the same answers as myhostname, so it doesn't
   make much sense to have myhostname at any other place than directly
   after resolve, so that if resolve is not available, we get answers for
   the names that myhostname is able to synthesize with the same priority.

See https://fedoraproject.org/wiki/Changes/systemd-resolved.

systemd.spec

@@ -627,7 +627,13 @@ function mod_nss() {
         # Add nss-systemd to passwd and group
         grep -E -q '^(passwd|group):.* systemd' "$1" ||
         sed -i.bak -r -e '
-                s/^(passwd|group):(.*)/\1: \2 systemd/
+                s/^(passwd|group):(.*)/\1:\2 systemd/
+                ' "$1" &>/dev/null || :
+
+        # Add nss-resolve to hosts
+        grep -E -q '^hosts:.* resolve' "$1" ||
+        sed -i.bak -r -e '
+                s/^(hosts):(.*) files( mdns4_minimal .NOTFOUND=return.)? dns myhostname/\1:\2 resolve [!UNAVAIL=return] myhostname files\3 dns/
                 ' "$1" &>/dev/null || :
     fi
 }