Use influxdb.ShardSpace instead of cluster.ShardSpace.

After fd45c925, compilation of daemon/influxd.go fails:

```
/usr/bin/go build -o influxdb -tags 'hyperleveldb rocksdb' github.com/influxdb/influxdb/daemon
# github.com/influxdb/influxdb/daemon
daemon/influxd.go:209: cannot use space (type *cluster.ShardSpace) as type *influxdb.ShardSpace in function argument
```

I'm not sure this is the right fix, but use of influxdb.ShardSpace fixes the error.