Replace the remnants of engine.cpp with better functionality in
FastBootDriver. Particularly, add prolog() and epilog()
callbacks to FastBootDriver for printing actions and their result to
the console. Then clean up the rest of fastboot.cpp to directly use
FastBootDriver.
Test: fastboot works
Change-Id: I0ff01d6a10f75e9dc1c82b46c6e9bb3bc4c68638
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
