Varnish 7 support - WIP

[cin]

Varnish-modules seem to be the main issue here. I'm having to build them from source and don't think I have them working with Varnish yet (haven't tested yet but not sure how it could work). There's also one more instance of varnish 6.x getting installed.

At the end of the day it'd be nice to support varnish 6.x and 7.x, but it appears that is going to be slightly painful since this build process is so divergent. May have to make separate dockerfiles to make it work.

Signed-off-by: Craig Ingram [email protected]