Package and storage movement callbacks.

Since package and primary storage movement can take quite awhile,
we want to have SystemUI surface progress and allow the Settings
app to be torn down while the movement proceeds in the background.

Movement requests now return a unique ID that identifies an ongoing
operation, and interested parties can observe ongoing progress and
final status.  Internally, progress and status are overloaded so
the values 0-100 are progress, and any values outside that range
are terminal status.

Add explicit constants for special-cased volume UUIDs, and change
the APIs to accept VolumeInfo to reduce confusion.  Internally the
UUID value "null" means internal storage, and "primary_physical"
means the current primary physical volume.  These values are used
for both package and primary storage movement destinations.

Persist the current primary storage location in MountService
metadata, since it can be moved over time.

Surface disk scanned events with separate volume count so we can
determine when it's partitioned successfully.  Also send broadcast
to support TvSettings launching into adoption flow.

Bug: 19993667
Change-Id: Ic8a4034033c3cb3262023dba4a642efc6795af10