fastbootd: erase "metadata" partition along with "erase userdata" command

On erasing userdata partition, all the related partitions (ex, metadata)
need to be erased respectively. Otherwise vold will get an error while
trying to decrypt the leftover materials on the next bootup.

Bug: 201533761
Test: fastboot erase userdata and reboot device
Change-Id: If299d43f6d8fc9e092d2229022abc29383698320
2 files changed