CLOUDSTACK-3590. Adding new xenserver host to cluster fails in first attempt. While adding

a host to the pool it may take a little longer to join the pool. Increased the time the
resource waits and checks to make sure the host has joined as slave to the pool.

plugins/hypervisors/xen/src/com/cloud/hypervisor/xen/resource/XenServerConnectionPool.java

@@ -197,7 +197,7 @@ public class XenServerConnectionPool {
                     }
                 }
                 try {
-                    Thread.sleep(2000);
+                    Thread.sleep(3000);
                 } catch (InterruptedException e) {
                 } 
             }