Update sigstore layout in (atomic sign)

[mtrmac]

Per containers/image#187 etc., containers/image#247 will change the sigstore layout from $base/$hostname/$repo-path/$image@$algo:$hex to $base/$repo-path/$image@$algo=$hex. Please update atomic sign accordingly.

The replacement of : with = is simple enough,

diff --git a/Atomic/sign.py b/Atomic/sign.py
index 57b851f..d41dfef 100644
--- a/Atomic/sign.py
+++ b/Atomic/sign.py
@@ -117,7 +120,7 @@ class Sign(Atomic):
                     if not os.path.exists(signature_path):
                         raise ValueError("The signature path {} does not exist".format(signature_path))
 
-                sigstore_path = "{}/{}@{}".format(signature_path, expanded_image_name.rsplit(':', 1)[0], manifest_hash)
+                sigstore_path = "{}/{}@{}".format(signature_path, expanded_image_name.rsplit(':', 1)[0], manifest_hash.replace(':', '=', 1))
                 self.make_sig_dirs(sigstore_path)
                 sig_name = self.get_sig_name(sigstore_path)
                 fq_sig_path = os.path.join(sigstore_path, sig_name)

but I’m not sure what to use instead of expanded_image so that the hostname is removed, especially considering that expanded_image may be resolved incorrectly (item 5 in #929).

[rhatdan]

@aweiteka PTAL

[mtrmac]

Fixed by #937.