Refined spring-oxm test execution check for compatibility with the recently announced JDK 9 version scheme

Issue: SPR-13012

build.gradle

@@ -556,7 +556,7 @@ project("spring-oxm") {
 		targetCompatibility = 1.6
 	}
 
-	if (System.getProperty("java.version").contains("1.9.")) {
+	if (!System.getProperty("java.version").contains("1.8.")) {
 		// necessary because castor and xjc tasks cannot find the JDK's compiler on JDK 9
 		compileTestJava.enabled = false
 	}