Revisit the close region related code at RS side

We use the closeRegion method to close a region and it will schedule a CloseRegionHandler(before HBASE-21217). The problem here is that, the CloseRegionHandler and closeRegion method are mainly designed to be called by master, but in fact, when shutting down RS, we will also call the closeRegion method to close all the regions on the RS.

In HBASE-21217, we change to use UnassignRegionHandler to close a region if the request is from master, so here we need to consider the close region request when shutting down RS.