Fix ca-less test to use X.509 v3 certificates

The generated certificates have been X.509 v1. This is not supported any
more. Only X.509 v3 is supported.

A new certificates/extensions.conf file has been added to make v3
certificates.

The existing certificates/pkinit/extensions.conf has been renamed to
certificates/pkinit-extensions.conf with additional changes. For example
"[kdc_cert]" had to be removed for v3.

The extensions config files are using environment variables, which are
set by the generate-certificates.sh script before calling openssl.

The script generate-certificates.sh has been reworked for a simpler
structure, also new options have been added: "ca" and "cleanup".