helper config for setting up a simple xenbr0 with dnsmasq

add a subpackage with a default lxcbr0 bridge interface with dnsmasq

This makes it very convenient to set up a private network for lxc
containers with a config that works out of the box.

Make it possible to create bridge interfaces for use with lxc and xen

create releases if there are new tags

refs #5082

needed by grub

neeed for ppc64le image

fixes #7066

we only support ffmpeg 3 now