Backport 'Move frontend virtualhost logic on backend'

This essentially aims to backport

nexedi/slapos!1435 and
nexedi/slapos!1504

to old slapos tag 1.0.249.

It also adds some more patches (that hopefully don't affect the
SR very much) to reduce merge conflicts.

Some patches are deliberately skipped:

1. nexedi/slapos@5b3fc1f2

We don't need this Zope backport fix, because this fix
aims to fix a patch that isn't even present in the Zope
we are using. See here for more context:

https://github.com/zopefoundation/Zope/issues/1191

2. nexedi/slapos@d49914a6

This seems to be a complex change that we may not need for
our purposes.

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Patches added:

33089cc2 software/erp5/test: Run tests with ZEO & NEO
81abed4e ERP5: rework frontend instance parameter
9abbfa08 software/erp5: describe the allowed formats for family and frontend names
2fe6f860 stack/erp5: remove not used "backend-path"
27a04553 stack/erp5: use slapos.recipe.build to manage haproxy parameters
cdadb774 stack/erp5: implement Zope's rewrite rules in ERP5 balancer partition