Drop pull_digest from hermetic boostrap image

Image has one Digest and many RepoDigests. So, we can hit situation
when these two values don't match and podman will refuse to load such
tarball later with error like described here:
containers/podman#27323

We should move to different mechanism (porbably skopeo) in the near
future.

Author: tkopecek

mock/py/mock-hermetic-repo.py

@@ -128,7 +128,7 @@ def prepare_image(image_specification, bootstrap_data, outputdir):
     Store the tarball into the same directory where the RPMs are
     """
     pull_cmd = ["podman", "pull"]
-    if "pull_digest" in bootstrap_data:
+    if bootstrap_data.get("pull_digest"):
         image_specification +=  "@" + bootstrap_data["pull_digest"]
     if "architecture" in bootstrap_data:
         pull_cmd += ["--arch", bootstrap_data["architecture"]]

mock/py/mockbuild/podman.py

@@ -251,13 +251,15 @@ def inspect_hermetic_metadata(self):
         """
         Get the image metadata needed for the subsequent hermetic build.
         """
-        get_query = '{"pull_digest": "{{ .Digest }}", "id": "{{.Id}}", "architecture": "{{ .Architecture }}"}'
+        get_query = '{"id": "{{.Id}}", "architecture": "{{ .Architecture }}"}'
         getLog().info("Reading image %s from %s", get_query, self.image)
         cmd = ["podman", "image", "inspect", "--format", get_query, self.image]
         res = subprocess.run(cmd, env=self.buildroot.env,
                              stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                              check=True)
-        return json.loads(res.stdout.decode("utf-8").strip())
+        res = json.loads(res.stdout.decode("utf-8").strip())
+        res['pull_digest'] = None
+        return res
 
 
     def __repr__(self):