assemblers/qcow2: Don't create extra level of tmp

Assemblers are always run in their own, clean environment and can be
sure that there's only one instance of themselves running. Remove the
extra layer of temporary directory and use static names.

assemblers/org.osbuild.qcow2

@@ -7,7 +7,6 @@ import os
 import socket
 import subprocess
 import sys
-import tempfile
 import osbuild.remoteloop as remoteloop
 
 def tree_size(tree):
@@ -50,11 +49,8 @@ def main(tree, output_dir, options, loop_client):
     filename = options["filename"]
     root_fs_uuid = options["root_fs_uuid"]
 
-    # Create a working directory on a tmpfs, maybe we should implicitly
-    # always do this.
-    with tempfile.TemporaryDirectory() as workdir:
-        image = f"{workdir}/image.raw"
-        mountpoint = f"{workdir}/mnt"
+    image = f"/tmp/osbuild-image.raw"
+    mountpoint = f"/tmp/osbuild-mnt"
 
     # Create an empty image file of the right size
     size = int(math.ceil(tree_size(tree) * 1.2 / 512) * 512)