daemon: Don't look for cockpit-*-admin groups

They will never be useful again.

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Don't check for cockpit-*-admin roles

Those roles will never exist again, and we need to check for polkit
actions instead in the future.

Reviewed-by: Stef Walter <stefw@redhat.com>
test: Use "docker" role instead of "cockpit-user-admin" in tests

Closes #1309
Reviewed-by: Stef Walter <stefw@redhat.com>