X-Fleet variable requires 'X-' prefix.
  - The older 'ConditionMachineOf' nomenclature requires 'X-'
  - Can also be updated to 'MachineOf' from v.0.8.0, but that
  doesn't match the rest of the documentation.
Moving X-Fleet variable to 'MachineOf'.
Merge pull request #329 from anonymuse/master

X-Fleet variable cleanup