Bind mount pkg specific dirs in the zygote child namespaces.

- Also update vold to create sandboxes for secondary storage devices.
- Since bind mounts are created in the process specific namespaces, we
  don't need /mnt/storage anymore which we were using it to prevent
  some bind mounts from propagating onto /mnt/runtime/write.
- Create bind mounts for {media,obb} dirs similar to data dir in
  per process namespace.
- Also fix a bug where we are not passing correct packages to vold when
  a new user starts.

Bug: 111890351
Test: manual
Change-Id: I7849efc4fbf3c654606fa30de7ab2de0236d766f
diff --git a/Utils.h b/Utils.h
index 48d605a..b097625 100644
--- a/Utils.h
+++ b/Utils.h
@@ -132,6 +132,8 @@
 
 status_t UnmountTree(const std::string& prefix);
 
+status_t DeleteDirContentsAndDir(const std::string& pathname);
+
 }  // namespace vold
 }  // namespace android