Fix varnish version in images

[davidalger]

See #480; this was a bug caused by Appstream pkg for varnish overriding the custom one from the Package Cloud repo with specific versions resulting in all the Varnish images having the default 4.0.x version from EL 8 rpms.

After these changes, the built images have the correct varnish versions once more:

$ docker run --rm -it wardenenv/varnish:6.5 varnishd -V
varnishd (varnish-6.5.2 revision e7233b0ad2639043341819d19a8d2e418e94ce1b)
Copyright (c) 2006 Verdens Gang AS
Copyright (c) 2006-2020 Varnish Software

$ docker run --rm -it wardenenv/varnish:6.4 varnishd -V
varnishd (varnish-6.4.0 revision 13f137934ec1cf14af66baf7896311115ee35598)
Copyright (c) 2006 Verdens Gang AS
Copyright (c) 2006-2020 Varnish Software AS

$ docker run --rm -it wardenenv/varnish:6.0 varnishd -V
varnishd (varnish-6.0.10 revision 9a7da4ff4c0c824af33e230740a11e99fdca23d9)
Copyright (c) 2006 Verdens Gang AS
Copyright (c) 2006-2021 Varnish Software

$ docker run --rm -it wardenenv/varnish:4.1 varnishd -V
varnishd (varnish-4.1.11 revision 61367ed17d08a9ef80a2d42dc84caef79cdeee7a)
Copyright (c) 2006 Verdens Gang AS
Copyright (c) 2006-2019 Varnish Software AS

[ihor-sviziev]

@davidalger great! Thank you!

[ihor-sviziev]

@davidalger I'd like to prepare arm versions of all the images (will start from varnish), based on what's available in this repo and in https://github.com/drpayyne/warden-multi-arch

So far everything is good preparing for varnish 6.0 and 6.5, but the versions 4.1 and 6.4 can't be built for some reason. So maybe better to just skip them for now. Will you accept it if I'll do a PR?