Crates are marked as build-fail even if they compile successfully

[pietroalbini]

rustc is providing an exit code of 1 even if there are no errors inside the Crater environment.

Example: https://crater-reports.s3.amazonaws.com/pr-53426-2/master%23fccde0018a618eb6f45d2a3c97f629809994dff6/reg/opcua-server-0.3.0/log.txt