Preserve app data if neither ce nor de have xattr user.default

For a given app, if xattr user.default is missing from both ce and de data
dirs, installd currently defaults to using ce.  However, if a system
app sets defaultToDeviceProtectedStorage="true" in it's manifest,
data is actually stored in de and so the effect is wipe for such
apps in the case where xattr user.default attributes are missing
(such as a tar backup/restore).

In the case where user.default is missing, if the app wants de
and the de dir exists then use it, otherwise, default to ce
as before.

Change-Id: I8d5583b7d156809b2aecc676db35e6bf7cad3e0c