Improve default Varnish config about appside

[ivomarino]

@ocean90 in order to do this we need to introduce some new {{ conf_varnish_* }} vars so first question is: what needs to be tuneable via vars and what features can directly be hardcoded into the configuration?

[ocean90]

Right, a few settings should be default and probably changeable via a config var.

Found another thing: Cookies are currently not removed from images. https://www.varnish-cache.org/lists/pipermail/varnish-misc/2011-February/019915.html should help for this.

[ocean90]

HAProxy has a balance option which is leastconn by default . I guess this makes sense for Apache but I found several posts which suggest uri for Varnish, see http://stackoverflow.com/a/16901584/3507335 and http://blog.haproxy.com/2012/08/25/haproxy-varnish-and-the-single-hostname-website/ (scroll to the Configuration section).
Thoughts on that?

https://cbonte.github.io/haproxy-dconv/configuration-1.6.html#4.2-balance