fix "cluster nodes" parse error when slot is in transition (fixes #635)

Though it's not documented, "cluster nodes" shows slot information being imported or migrated.

Below is src/cluster.c from latest Redis unstable branch.
````
    /* Just for MYSELF node we also dump info about slots that
     * we are migrating to other instances or importing from other
     * instances. */
    if (node->flags & REDIS_NODE_MYSELF) {
        for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
            if (server.cluster->migrating_slots_to[j]) {
                ci = sdscatprintf(ci," [%d->-%.40s]",j,
                    server.cluster->migrating_slots_to[j]->name);
            } else if (server.cluster->importing_slots_from[j]) {
                ci = sdscatprintf(ci," [%d-<-%.40s]",j,
                    server.cluster->importing_slots_from[j]->name);
            }
        }
    }
````

So Jedis should able to parse it.

Btw, module that parses cluster nodes information could be complicated, so I've refactored to move to another class.

* extract cluster nodes info. parser from JedisClusterConnectionHandler
** ClusterNodeInformation & ClusterNodeInformationParser
** user can use it with "cluster nodes" command result, not only JedisClusterConnectionHandler
* unit test for migrating slot included