* update compute instance docs to use new boot and scratch disk attributes, document attached_disk
* Update compute instance tests to mostly use new boot and scratch disk attributes
* Fix encryption test by setting values in state from what was there before
* Add scratch_disk property to google_compute_instance
* docs for scratch_disk
* limit scope of scratchDisks array by using bool, test formatting
* add slash back to disk check
* Add boot_disk property to google_compute_instance
* docs for boot_disk
* limit scope of bootDisk, use bool instead
* test formatting
* make device_name forcenew, add sha256 encryption key
