increase sleep before testing detach. The VM must be completely up. (#417)

Author: k0ka

tests/sample/Compute/v2/VolumeAttachmentTest.php

@@ -70,7 +70,7 @@ public function testDetach(VolumeAttachment $createdVolumeAttachment)
         // let's wait for the server to be completely up
         // https://bugs.launchpad.net/nova/+bug/1998148
         // https://bugs.launchpad.net/nova/+bug/1960346
-        sleep(15);
+        sleep(30);
 
         require_once $this->sampleFile(
             'volume_attachments/delete.php',