add locateRegions to HBaseClient

1. add locateRegions(byte[] tableName) to HBaseClient, this method
   returns RegionInfo for all table regions as long as hostname and
   port.
2. add RegionLocation class, which represents RegionInfo + host:port
3. make RegionInfo public

Change-Id: Ieb41ac2a4526c825e08a44b3425a63c802b72df7