message: fix sync problem when call net_plugin::disconnect
diff: using namespace appbase;
  using namespace eosio;
  +static std::shared_ptr<std::mutex> m(new std::mutex());
  +static std::shared_ptr<std::condition_variable> cv(new std::condition_variable());
  +
  net_plugin& get_net_plugin() {
  abstract_plugin& plugin = app().get_plugin<eosio::net_plugin>();
  return *static_cast<net_plugin*>(&plugin);
  @@ -21,8 +24,18 @@ string connect_(const string& host) {
  }
  string disconnect_(const string& host) {
  - return get_net_plugin().disconnect( host );
  + std::shared_ptr<string> result = std::make_shared<string>();
  +
  + appbase::app().get_io_service().post([result, host](){
  + *result = get_net_plugin().disconnect( host );
  + cv->notify_one();
  + });
  +
  + std::unique_lock<std::mutex> lk(*m);
  + cv->wait(lk);
  + return *result;
  }
  +
  PyObject* status_(const string& host) {
  auto s = get_net_plugin().status( host );
  return python::json::to_string(fc::variant(s));
  