Automatically use correct lower paths for setupAppDir.

When we're asked to create an app directory, find the corresponding
volume, and use the raw path of that volume to create the directory.
This ensures this will continue working on devices that don't have
sdcardfs.

Bug: 146419093
Test: manual test on cuttlefish
Change-Id: I91d735c1adbcca171e5af73aca0abd7ef396d0b7
diff --git a/model/Disk.h b/model/Disk.h
index 889e906..d82d141 100644
--- a/model/Disk.h
+++ b/model/Disk.h
@@ -67,6 +67,8 @@
 
     void listVolumes(VolumeBase::Type type, std::list<std::string>& list) const;
 
+    std::vector<std::shared_ptr<VolumeBase>> getVolumes() const;
+
     status_t create();
     status_t destroy();