CI: dump OpenDJ container logs when Docker image smoke tests fail

The build-docker and build-docker-alpine jobs start the packaged image and
probe it over LDAP, but never captured the container's own output. A failed
"Docker test" / "Docker test custom password" step therefore showed only the
client-side LDAP error (e.g. 32 No Such Entry, 81 Server Connection Closed)
with no visibility into run.sh / bootstrap/setup.sh, which run inside the
container and are where base-entry creation and startup actually happen.

Add an ERR trap to each of the four docker test steps that dumps
`docker logs` for the relevant container (test / test_custom) inside a
collapsible group and re-exits with the original status. The step still
fails exactly as before, but now with the container's setup output attached.