* Rename deviceinfo variable flash_methods to flash_method
* Update pmb.config.deviceinfo_attributes / add sanity check
* Add test case that parses all deviceinfo files
This adds a new deviceinfo 'flash_fastboot_max_size' used for
preventing fastboot from flashing a system partition that is too
large. Some devices do not support flashing over a certain size
(e.g. 500MB).
