core: Basic MachineIndex class, starting point
core: MachineIndex has precision locking for entries
core: replace "-" in UUIDs with ""
core: Add MachineIndex#delete
core: Environment#machine_index
core: Machine sets index entries on ID sets
core: Machine updates state cache when querying state
core: MachineIndex is enumerable
commands/global-status: initial go at it
core: Use Machine#state wherever possible so we update the index
core: commands can use the IDs from anywhere to control
core: Silence ruby warnings when loading external machines
core:  pass along the UI class so we don't get a silent UI
Merge pull request #3225 from mitchellh/f-centralized-machines

Centralized machine index