Bug #884018: "stack help" prints stacktrace if it cannot connect to the server

Add a handler for URLError, so that we print a nicer error message if stack
cannot connect to the server.

Change-Id: I24f977dcb12bee3bb21057fe9b19823d98581141

bin/stack

@@ -118,6 +118,9 @@ def do_request(controller, method, params=None):
     req = urllib2.Request(url, data, headers)
     try:
         resp = urllib2.urlopen(req)
+    except urllib2.URLError, e:
+        print 'Failed to connect to %s: %s' % (url, e.reason)
+        sys.exit(1)
     except urllib2.HTTPError, e:
         print e.read()
         sys.exit(1)