Procedure v2 - A couple of tweaks to the SplitTableRegionProcedure

Make a couple of tweaks to HBASE-14551 split procedure

• remove tableName from SplitTableRegionProcedure ctor since we have the RegionInfo that contains the name already
• move the checkRow in the constructor of the SplitTableRegionProcedure, since the splitRow will never change and we can avoid to start the proc if we have a bad splitRow.
• use the base AbstractStateMachineTableProcedure for the "user" field
• remove protobuf fields that can be extrapolated from other info (table_name, split_row)
• avoid htd lookup every family iteration of splitStoreFiles()