Keep metadata of documents as disconnected status after the device is

disconnected.

To restore Document IDs when the device is reconnected, we need to keep
the metadata in database so that we can use it as hint to remap document
ID with new MTP IDs.

BUG=26212981

Change-Id: Idcc93c41c09d082a709281022c56188dabc80515
(cherry picked from commit 53f5af3f)