Even with Insecure registry=theregistry, (which basically disables tls verfication from docker daemon side, we still get a not found.
DEBU[0088] Calling POST /images/create
DEBU[0088] Pulling tag from V2 registry: "latest"
DEBU[0088] Error trying v2 registry: Error parsing HTTP response: invalid character '<' looking for beginning of value: "<!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML 2.0//EN\">\n<html><head>\n<title>404 Not Found</title>\n</head><body>\n<h1>Not Found</h1>\n<p>The requested URL /pulp/docker/v2/busybox/manifests/latest was not found on this server.</p>\n</body></html>\n"
DEBU[0088] Not continuing with error: Error: image pulpdemo/busybox:latest not found