Implement issue #3094621 and #3094609 - wipe sd card

3094621: add "wipe sd card" option to factory data reset
3094609: collapse unmount/format into one command

Also since we have decided that it is important to consider
the Crespo storage as internal storage, DevicePolicyManager
gets a new API to be able to wipe it.  (No big deal, since
all of the work for this is now done in the implementation
of the new UI.)

Change-Id: I32a77c410f710a87dcdcbf6586c09bd2e48a8807