Review Request: JDK-8168836 Minor clean up on warning/error messages on --add-exports and --add-reads

[Mandy Chung]

http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8168836/webrev.00/

This patch improves the warning/error message to include the option name, emit 
a warning if unknown module is specified with —-patch-module be consistent with 
the options.

Mandy