'docker trust sign' does not work with manifest lists #910
Description
I created/pushed a new manifest list (using some LinuxKit images/repo for which signing is already set up:
$ docker manifest create linuxkit/auditd:test-sign \
linuxkit/auditd:6ea41e1a0c3c0396703aa888f23e5dafcc4fd2bd-arm64 \
linuxkit/auditd:6ea41e1a0c3c0396703aa888f23e5dafcc4fd2bd-amd64
$ docker manifest push linuxkit/auditd:test-sign
The manifest is available and inspectable.
The, I attempt to sign the manifest list:
$ docker trust sign linuxkit/auditd:test-sign
Error: No such image: linuxkit/auditd:test-sign