RFR (S) round 0 for 8141068 Refactor -XXFlags= code in preparation for removal

[Gerald Thornbrugh]

Hi Ron,

Your changes look good.

Jerry
> This bug fix consists of a refactoring/cleanup of the -XX:Flags code.
>
> Webrev:
> http://cr.openjdk.java.net/~rdurbin/8141068_OCR0_JDK9_webrev
>
>
> Bug report:
> https://bugs.openjdk.java.net/browse/JDK-8141068
>
> This bug fix has been tested on:
>     OS:
>       Solaris, MAC, Windows, Linux
>     Tests:
>       Manual unit tests
>       JPRT with -testset hotspot(including the SQE current test coverage for this feature.)