System.getProperty("java.home") should have the precedence over $JAVA_HOME (at least Gradle itself does this)

[mauromol]

Please see: #33 (comment)

If Gradle finds the java.home system property set (for example by virtue of org.gradle.java.home property set on $GRADLE_USER_HOME/gradle.properties), it uses this to locate the Java compiler to use to compile Java sources, instead of $JAVA_HOME.

I think the jnlp plugin should do the same to run the Pack200 executable. This should ensure better consistency between compilation and post-processing of signed JAR files for packing purposes.

Right now, it does exactly the opposite ($JAVA_HOME takes precedence).