This change creates a nice and clean API for issuing
fastboot commands without using the fastboot tool itself.
Test: fastboot tool itself (now using libfastboot2)
on sailfish, walleye, and other devices.
Test: flash bootloader bootloader.img
Test: flash radio radio.img
Test: -w update img.zip
Test: Manually getvar and reboot commands.
Bug: 111126621
Change-Id: I0022536b204ce0c5ad8329367fd522fa3c57877d
Also switch all remaining headers over to #pragma once, and actually
use FB_COMMAND_SZ.
Bug: http://b/77340848
Test: ran tests
Change-Id: I27107d054c206e66c39208099e36a55df604e08f