events: ensure_server blocks app on startup

Client blocks on startup, before a single line of debug has appeared. After some seconds of block, SIGINT gives me this bt:

samsara 戝 ~leapsrc ➤ 8f3e733|develop✓
10580 ± : python app.py --debug --danger                                                                                                                       ⏎ [1h48m]
^CTraceback (most recent call last):
  File "app.py", line 216, in 
    main()
  File "app.py", line 134, in main
    event_server.ensure_server(event_server.SERVER_PORT)
  File "/home/kali/Virtualenvs/leap-client/local/lib/python2.7/site-packages/leap.common-0.2.7-py2.7.egg/leap/common/events/server.py", line 80, in ensure_server
    response = ping(port)
  File "/home/kali/Virtualenvs/leap-client/local/lib/python2.7/site-packages/leap.common-0.2.7-py2.7.egg/leap/common/events/server.py", line 115, in ping
    return service.ping(request, callback=reqcbk, timeout=timeout)
  File "/home/kali/Virtualenvs/leap-client/local/lib/python2.7/site-packages/protobuf.socketrpc-1.3.2-py2.7.egg/protobuf/socketrpc/service.py", line 114, in 
    timeout, callback)
  File "/home/kali/Virtualenvs/leap-client/local/lib/python2.7/site-packages/protobuf.socketrpc-1.3.2-py2.7.egg/protobuf/socketrpc/service.py", line 194, in call
    rpc_thread.join(timeout)
  File "/usr/lib/python2.7/threading.py", line 958, in join
    self.__block.wait(delay)
  File "/usr/lib/python2.7/threading.py", line 358, in wait
    _sleep(delay)
KeyboardInterrupt
(leap-client)

(from redmine: created on 2013-08-01, closed on 2013-08-16, relates #3276 (closed))