Of course, only one of these ...ScriptEngineFactory classes can be correct. Therefore, on Java 7 you get a CNFE for the 2nd line, and on Java 8 already for the 1st line. But a matching service class is found in both cases.

The message line in server.log for Java 7:
ERROR [stderr] ScriptEngineManager providers.next(): javax.script.ScriptEngineFactory: Provider jdk.nashorn.api.scripting.NashornScriptEngineFactory not found

Maybe the message should be a warning (and not an error) as e.g. for RESTEasy:
WARN  [org.jboss.resteasy.plugins.providers.RegisterBuiltin] NoClassDefFoundError: Unable to load builtin provider: org.jboss.resteasy.security.smime.MultipartSignedReader