Makefile/._state cache can be stale; glue it in more tightly with Vagrantfile/ruby hooks

[ssenator]

record machine's GUID into the state file
If the GUID doesn't exist, invalidate that state file
If a machine with that name and GUID exists, report EX_ALREADY or EX_OK (context defines)
If a machine with that name and a different GUID exists, EX_CANTCREAT, EX_TEMPFAIL, EX_ALREADY