slapos.core now depends on PyYAML and jsonschema

This upgrade fixes deadlock when new context is created from
already-canceled parent[1]. It also comes with other minor enhancements
and fixes needed e.g. for `zodb restore`[2].

[1] nexedi/pygolang@58d4cbfe
[2] https://pypi.org/project/pygolang/#pygolang-change-history

json-c, memcached and xpdf are still maintained but current
buildout.cfg are not useful if we want to ship a new version.

Keep compatibility with the default webrunner configuration.

Prevent unexpected instance deletion.

See merge request !1094

It appears no longer needed to use LD_LIBRARY_PATH to ensure the
correct runtime path resolution of libsecret in theia's `keytar`
component. Also LD_LIBRARY_PATH was leaking into theia's environment
and affecting tests launched from within theia.

This reverts commit 681ec188.

See merge request !1096

Always format the partitions to ensure the slapformat configuration is
valid, because the constructor overwrites it with invalid values.

We need a valid configuration so that `slapos node format` works,
and we need `slapos node format` for the resiliency import script.

No need for the full URL here

This will force a password reset

Aggregate monitoring URLs from the main theia, clones and PBS.

Also add monitor-setup-url to the parameters published by the PBS.

32fbf0d4 (recipe/postgres: support non standard port, 2021-11-12)
broke support for empty port, it was generating config file with
`port = ` , which is an invalid config file syntax for postgresql.