Fixes problem described in https://bugzilla.redhat.com/show_bug.cgi?id=2079938

Support absolute and relative paths. Paths starting with "rbd:" are special,
and they point to the rbd endpoint, served by Ceph.

cache parameter is optional, in case if present, will be used as-is, even with
empty cache.

external-disk-number, external-disk-size and external-disk-format has been
removed from the schema to become hidden, nevertheless it's expected to be
fully supported, as long tests are kept.

Loudly fail in case if old and new ways are used in the same time.

Switch to pure meson build system and adapt configuration for SlapOS
requirements.

Support multiarch env by simply linking from lib64.

Version 249.6 incorporates fix from https://bugs.gentoo.org/824026 for:
  meson.build: ERROR: Object <[BooleanHolder] holds [bool]: False> of
  type bool does not support the +

This was removed from ERP5 in d9be34803b (erp5-util: remove zodbanalyze,
that is now a part of https://lab.nexedi.com/nexedi/zodbtools ., 2016-12-15)
but we were still installing a broken script here.

using ./format-json script

From now on, hosts keys will always be checked and there is no way
to disable the check