Explicitly request clearing of external storage.

Similar to how we target DE and CE storage areas, callers need to
specifically ask to work with EXTERNAL storage.  This is because
external storage often lives on a separate device from where internal
DE and CE data lives.

As one specific example, if we're moving an app between two
"internal" storage devices, we don't want to clean up the data
for that package on external storage, since it's not being moved.

This change also expands to all mounted external storage devices,
not just the storage backed by the incoming UUID.

Bug: 113277754
Test: atest android.appsecurity.cts.StorageHostTest
Test: atest android.appsecurity.cts.ExternalStorageHostTest
Test: atest --test-mapping frameworks/base/services/core/java/com/android/server/pm/
Change-Id: Ie125303726dd757ee45bd373f53addb35569c2f7