This description is required when requesting more than one zope partition
sharing a given IP (ex: webrunner-type setup).

- There's now a single software type 'neo' (in addition to the default)
  which contains:
  - 1 master
  - 1 admin
  - a configurable number of storage nodes, that share the same MySQL server
- Review of parameters to configure MySQL server.
  (innodb_buffer_pool_size is important)
- Check of meaningless values of 'replicas'.

This reverts commit bf75e8a9.

also parallel build becomes possible again.

Ruby2.1

To support GitLab we need current Ruby oldstable, which is Ruby 2.1.6.

Rationale: https://gitlab.com/gitlab-org/gitlab-ce/commit/757df0142f521380b92d28a721a7fd2bd8aa382f

/cc @kazuhiko

See merge request !5

Current Ruby stable is 2.2.2, but current GitLab does not work with it,
and requires current Ruby oldstable, which is 2.1.6:

    https://gitlab.com/gitlab-org/gitlab-ce/commit/757df0142f521380b92d28a721a7fd2bd8aa382f

/cc @kazuhiko

In the next patch we'll add another version of Ruby, and it will make
sense to share common configuration for Ruby compiling.

/cc @kazuhiko