Adds a test case for installing a plugin from a remote in the form
of `plugin-content-trust@sha256:d98f2f8061...`, which is currently
causing the daemon to panic, as we found while running the CLI e2e
tests:
```
docker plugin install registry:5000/plugin-content-trust@sha256:d98f2f806144bf4ba62d4ecaf78fec2f2fe350df5a001f6e3b491c393326aedb
```
Signed-off-by: Laura Brehm <laurabrehm@hey.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
2dc6b50863