* remove outdated references to envchain in documentation
* add new host volume locations in userdata
* don't exit the entire script during provisioning, just return
This changeset stages upcoming E2E provisioning improvements work. It splits
the existing shared configuration directory into 3 profiles:
* "full-cluster": the set of configurations currently in use
* "dev-cluster": a simplified set of mostly existing configurations that
weren't in use.
* "custom": an empty profile for developers to keep non-standard
configurations during complex feature development.
The tooling to switch between profiles will be in a later changeset.
Also drops some unused configuration knobs from the provisioning scripts to
make the next stage of work easier.
