fix: keep puppetserver gems out of the var-dir mount path

[slauger]

Problem

The bundled puppetserver.conf points master-var-dir at /opt/puppetlabs/server/data/puppetserver -- the same directory that holds the static, image-provided jruby-gems and vendored-jruby-gems (where require 'puppet' is loaded from).

To persist variable runtime data (yaml, server_data, bucket, reports) people mount a volume on data/puppetserver. That overlays and empties the gem directories, so the server can no longer load Puppet and dies with:

LoadError: no such file to load -- puppet

The entrypoint only restores vendored-jruby-gems, not jruby-gems, so that workaround is incomplete.

Fix

Point master-var-dir at a dedicated .../puppetserver/var sub-directory. The variable data now has its own mountable location, and the gems stay untouched at their absolute paths. gem-home / gem-path are already absolute and are not derived from the var-dir, so they are unaffected.

• openvoxserver/files/etc/puppetlabs/puppetserver/conf.d/puppetserver.conf: master-var-dir -> .../puppetserver/var
• openvoxserver/prep_build_container.sh: create the new var directory (ownership is already handled by the recursive chown on data/puppetserver)

Applies to both the Ubuntu and Alpine images via the shared prep scripts.

Verification

Built the Ubuntu image and ran, as the puppet user:

Mount	require 'puppet'
none (baseline)	OK (8.27.0)
empty volume on .../puppetserver/var	OK (8.27.0)
empty volume on .../puppetserver	LoadError: no such file to load -- puppet

So the new var dir is freely mountable without clobbering the gems, and the old foot-gun is reproduced as the control. This also makes running with a read-only root filesystem viable.

Breaking change

This changes the default master-var-dir location. Existing deployments that persist or mount variable data at /opt/puppetlabs/server/data/puppetserver will need to move that mount to /opt/puppetlabs/server/data/puppetserver/var. Data previously persisted at the old path will not be picked up automatically.

Follow-up

The Helm chart most likely needs a matching change. It currently mounts a volume over the whole data/puppetserver directory, which is exactly what triggers the LoadError and what this PR makes unnecessary. That mount should be moved to .../puppetserver/var (or dropped in favour of persisting only what actually needs it). Happy to follow up there.