Issue 694: Correcting unit test to run it single-threaded

compute/src/test/java/org/jclouds/compute/callable/RunScriptOnNodeUsingSshTest.java

@@ -38,7 +38,7 @@ import static org.jclouds.scriptbuilder.domain.Statements.exec;
 /**
  * @author Adam Lowe
  */
-@Test(groups={"unit"})
+@Test(groups={"unit"}, singleThreaded = true)
 public class RunScriptOnNodeUsingSshTest  {
     private SshClient sshClient;
     private NodeMetadata node;