RFR 8153238: Improve test/tools/jlink/JLinkTest.java not to hard code the number of plugins

[Mandy Chung]

> On Jun 24, 2016, at 9:54 AM, Sundararajan Athijegannathan <sundararajan.athijegannathan at oracle.com> wrote:
> 
> Please review http://cr.openjdk.java.net/~sundar/8153238/webrev.00/ for
> https://bugs.openjdk.java.net/browse/JDK-8153238

  86             if (builtInPlugins.size() < numPlugins) {

What about just count the plugins defined in jdk.jlink module (i.e. matching what getNumJlinkPlugins counts)?

Since you are on this file, -verbose:gc is not needed for a test.  Maybe good to take this out.

  56  * @run main/othervm -verbose:gc -Xmx1g JLinkTest

Mandy