Adding systemd-resolvconf

configs/releng/packages.x86_64:
Due to dropping netctl from the image, no packgae currently directly
pulls in a resolvconf provider.
The systemd-resolvconf package is compatible with systemd-resolved which
is in use on the image now and the preferred choice.

Closes #22

configs/releng/packages.x86_64

@@ -60,6 +60,7 @@ sdparm
 sg3_utils
 smartmontools
 sudo
+systemd-resolvconf
 tcpdump
 testdisk
 usb_modeswitch