This update fixes the following issues for nss-mdns:
- Add nss-mdns-config script as a source, and install it in /usr/sbin: this script can be used to enable/disable mdns in /etc/nsswitch.conf (-4/-6 can be used to restrict enabling/disabling to IPv4/IPv6).
- Change %post/%preun scriptlets to use new nss-mdns-config script instead of custom perl-fu.
- Do not restrict mdns support in /etc/nsswitch.conf to IPv4: just pass --enable to nss-mdns-config in %post. Fix bnc#710231.
- Only call nss-mdns-config in %post on first install, to avoid overwriting changes done by users. Fix nss-mdns side of bnc#729796.
- Do not call sed to change /etc/nsswitch.conf to remove services not provided by nss-mdns anymore: when we need this, we'll be able to integrate this in nss-mdns-config.