libsnapshot: Error handling after QuerySnapshotStatus

QuerySnapshotStatus will capture the error codes
from dm-snapshot if there are any snapshot related
failure. Handle the error codes and fail the
QuerySnapshotStatus call.

Validate snapshot status in MapSnapshot(). If
the mode is set to Persistent and snapshot status
is in Merging state, then forcefully set the
mode to Merge state.

Bug: 198265278
Test: Full/incremental OTA
Signed-off-by: Akilesh Kailash <akailash@google.com>
Change-Id: I779184f1998b23edacd6e780acf2676442004340
Merged-In: I779184f1998b23edacd6e780acf2676442004340