GEODE-5620: Adds project property to control test forking

Fixing testMaxParalleForks property handling.  The code was using
the character code for the number assigned to the property.  It needed
to parse the value to turn it into the requested number.

gradle/test.gradle

@@ -87,7 +87,7 @@ subprojects {
       TestPropertiesWriter.writeTestProperties(buildDir, name)
     }
     if (project.hasProperty('testMaxParallelForks')) {
-      maxParallelForks = project.testMaxParallelForks
+      maxParallelForks = Integer.parseUnsignedInt(project.testMaxParallelForks)
     } else {
       maxParallelForks = Runtime.runtime.availableProcessors().intdiv(2) ?: 1
     }