Improve create keyspace performance

[rleungx]

Enhancement Task

When we create a keyspace, we first write a region label to etcd, then wait for the scheduling service to finish the split region operation. But the performance could be limited by the patrol region time. Only when a region is scanned and the split checker will create an operator, which is slow if we have too many regions in a large cluster. One possible way is to add the corresponding region to suspect regions to reduce the time cost of scanning the region.