Same as commit 8da9aa07, to reduce redundancy.

Was accidentally lost, and documented as the intended value - though it is
not.

Documentation now lives in json schemas.

Drop instance-erp5-single and instance-zope:
All deployments of ERP5 instances must be covered by cluster-style
deployment, and tweaked by parameters rather than software type.
Drop instance-varnish:
This is not used currently, so avoid giving the impression that it is
supported. Revive when properly integrated.

Only able to use a pre-existing NEO cluster.

Better failing than silently ignoring a missing parameter because of a
typo. Only parameters provided by users should be allowed to be missing,
not internal ones.

This value is used as a directory name, so we should follow the common
denominator.

Also, follow naming convention.

vincent: Minor fixes. Move branch switch to a separate commit.
vincent: Provide configuration to mysql_install_binary.

Loosened checks are considered safe enough, and the speedup on many-GB
FileStorage files is significant.

Split line more naturally (don't separate switch from related argument).
Use long options instead of abbreviations.

Also, reduce code duplication.

By don't creating the inituser file if it has already been done once.

disable FIPS explicitly, otherwise stunnel fails to start with the following output :

Threading:PTHREAD Sockets:POLL,IPv6 SSL:ENGINE,OCSP,FIPS
Reading configuration from file etc/stunnel.conf
FIPS_mode_set: F06D065: error:0F06D065:common libcrypto routines:FIPS_mode_set:fips mode not supported
Line 5: "[remote]": Failed to initialize SSL