vold: implement resetCheckpoint

It will be used by userspace reboot to reset checkpoint state, to make
sure that when /data is remounted, it will be remounted in checkpointing
if a checkpoint was requested beforee userspace reboot.

Test: /system/bin/vdc startCheckpoint 1
      /system/bin/vdc needsCheckpoint (returns 0)
      /system/bin/vdc resetCheckpoint
      /system/bin/vdc needsCheckpoint (returns 1)

Bug: 135984674
Change-Id: Ia29238686289b4eed93e2fb936a8b3d894b94dc9
diff --git a/VoldNativeService.h b/VoldNativeService.h
index 07a0b9f..13137c5 100644
--- a/VoldNativeService.h
+++ b/VoldNativeService.h
@@ -140,6 +140,7 @@
     binder::Status supportsCheckpoint(bool* _aidl_return);
     binder::Status supportsBlockCheckpoint(bool* _aidl_return);
     binder::Status supportsFileCheckpoint(bool* _aidl_return);
+    binder::Status resetCheckpoint();
 };
 
 }  // namespace vold