Add vdc checkpoint restoreCheckpointPart

Restores the first n entries of a checkpoint. Allows automated testing
of interrupted restores.

Test: vdc checkpoint restoreCheckpoint [device] [n]
Change-Id: I47570e8eba0bc3c6549a04a33600df05d393990b
diff --git a/Checkpoint.h b/Checkpoint.h
index 64ceed3..70dad8a 100644
--- a/Checkpoint.h
+++ b/Checkpoint.h
@@ -37,7 +37,7 @@
 
 android::binder::Status cp_prepareCheckpoint();
 
-android::binder::Status cp_restoreCheckpoint(const std::string& mountPoint);
+android::binder::Status cp_restoreCheckpoint(const std::string& mountPoint, int count = 0);
 
 android::binder::Status cp_markBootAttempt();