mounts: include tree directory in arguments

Include the path to the tree for all mount services, so that future
services can e.g. bind mount something inside the tree.

osbuild/mounts.py

@@ -63,9 +63,11 @@ class MountManager:
 
         args = {
             "source": source,
-            "root": self.root,
             "target": mount.target,
 
+            "root": self.root,
+            "tree": self.devices.tree,
+
             "options": mount.options,
         }