- Vagrantfile: Correct the path to the parsed YAML file. (This caused
  'vagrant global-status' to fail when called from outside the project's
  directory.)

- Vagrantfile: As we do not use it, disable the default sharing of the
  project's directory with the VMs.

- lockss: Use /tmp as temporary directory.

- Other trivialities.

When it already exists, the swap file managed by the role must be
excluded from the sum of memory and swap used to calculate the size of
said file.

The size of the swap file's header ought to be included in the
calculation; otherwise, the file will be slightly undersized, and the
role will re-create it at every invocation.