fixed unit test to be single-threaded as mocks aren't threadsafe

compute/src/test/java/org/jclouds/compute/predicates/NodePredicatesTest.java

@@ -34,7 +34,7 @@ import org.testng.annotations.Test;
  * 
  * @author Aled Sage
  */
-@Test
+@Test(singleThreaded = true, testName = "NodePredicatesTest")
 public class NodePredicatesTest {
 
    private NodeMetadata node;