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.cpp b/model/Disk.cpp
index b66c336..f8357a9 100644
--- a/model/Disk.cpp
+++ b/model/Disk.cpp
@@ -162,6 +162,17 @@
     }
 }
 
+std::vector<std::shared_ptr<VolumeBase>> Disk::getVolumes() const {
+    std::vector<std::shared_ptr<VolumeBase>> vols;
+    for (const auto& vol : mVolumes) {
+        vols.push_back(vol);
+        auto stackedVolumes = vol->getVolumes();
+        vols.insert(vols.end(), stackedVolumes.begin(), stackedVolumes.end());
+    }
+
+    return vols;
+}
+
 status_t Disk::create() {
     CHECK(!mCreated);
     mCreated = true;