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/vdc.cpp b/vdc.cpp
index 839e70e..c1b7781 100644
--- a/vdc.cpp
+++ b/vdc.cpp
@@ -147,6 +147,8 @@
         int retry;
         if (!android::base::ParseInt(args[2], &retry)) exit(EINVAL);
         checkStatus(args, vold->abortChanges(args[2], retry != 0));
+    } else if (args[0] == "checkpoint" && args[1] == "resetCheckpoint") {
+        checkStatus(args, vold->resetCheckpoint());
     } else {
         LOG(ERROR) << "Raw commands are no longer supported";
         exit(EINVAL);