objectstore: eagerly unmount bind-mounts

In the object store, temporary bind mounts are used when accessing the
content, i.e. the individual trees. Their unmount is currently done
with the `--lazy` flag. The use of this flag goes way back to commit
da121beda1, which sadly does not mention
why the flag was introduced. Since the tree and files in the tree will
be used by consequent stages it seems reasonable to do the un-mounting
eagerly and thus this reverts back to that behavior.

osbuild/objectstore.py

@@ -44,7 +44,7 @@ def mount(source, target, bind=True, ro=True, private=True, mode="0755"):
         raise RuntimeError(f"{msg} (code: {code})")
 
 
-def umount(target, lazy=True):
+def umount(target, lazy=False):
     args = []
     if lazy:
         args += ["--lazy"]