start mesos scheduler driver

This should fix https://github.com/mesos/storm/issues/3
How about something like this:

```java
  @Override
  public void prepare(Map conf, String localDir) {
    try {
      _conf = conf;
      _state = new LocalState(localDir);
      String id = (String) _state.get(FRAMEWORK_ID);

      _allowedHosts = listIntoSet((List) _conf.get(CONF_MESOS_ALLOWED_HOSTS));
      _disallowedHosts = listIntoSet((List) _conf.get(CONF_MESOS_DISALLOWED_HOSTS));

      Semaphore initter = new Semaphore(0);
      _scheduler = new NimbusScheduler(initter);
      Number failoverTimeout = (Number) conf.get(CONF_MASTER_FAILOVER_TIMEOUT_SECS);
      if (failoverTimeout == null) failoverTimeout = 3600;

      String role = (String) conf.get(CONF_MESOS_ROLE);
      if (role == null) role = new String("*");
      Boolean checkpoint = (Boolean) conf.get(CONF_MESOS_CHECKPOINT);
      if (checkpoint == null) checkpoint = new Boolean(false);

      FrameworkInfo.Builder finfo = FrameworkInfo.newBuilder()
          .setName("Storm!!!")
          .setFailoverTimeout(failoverTimeout.doubleValue())
          .setUser("")
          .setRole(role)
          .setCheckpoint(checkpoint);

      if (id != null) {
        finfo.setId(FrameworkID.newBuilder().setValue(id).build());
      }

      _httpServer = new LocalFileServer();
      _configUrl = _httpServer.serveDir("/conf","conf");
      LOG.info("Started serving config dir under " + _configUrl);

      MesosSchedulerDriver driver =
          new MesosSchedulerDriver(
              _scheduler,
              finfo.build(),
              (String) conf.get(CONF_MASTER_URL));

      driver.start();
      LOG.info("Waiting for scheduler to initialize...");
      initter.acquire();
      LOG.info("Scheduler initialized...");
    } catch (Exception e) {
      throw new RuntimeException(e);
    }
  }
```