Progress towards FBE and adoptable storage.

Offer to adopt storage devices on FBE devices, but keep it guarded
behind a system property for now, since we still need to work out key
storage details.

Verify that all users are unlocked before moving apps or shared
storage.  We only need them to be unlocked; we don't need them to
be actually running.

Have PackageManager dump the set of volumes that it's finished
scanning and loading, since otherwise CTS can get excited and race
too far ahead of it.  Add a specific error code to communicate
that users are locked.

Test: cts-tradefed run commandAndExit cts-dev --abi armeabi-v7a -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.AdoptableHostTest
Bug: 37436961, 29923055, 25861755, 30230655
Change-Id: I749dc3d8148e1a95d8bc4be56665253ef826d3fe