Keep priority on scanner's subsequent scans

If a scanner needs to scan multiple times ensure all scanners get the
priority set in the initial hrpc.Scan.

scanner.go

@@ -211,12 +211,18 @@ func (s *scanner) request() (*pb.ScanResponse, hrpc.RegionInfo, error) {
 			s.rpc.Options()...)
 	} else {
 		// continuing to scan current region
+		var priority uint32
+		if p := s.rpc.Priority(); p != nil {
+			priority = *p
+		}
 		rpc, err = hrpc.NewScanRange(s.rpc.Context(),
 			s.rpc.Table(),
 			s.startRow,
 			nil,
 			hrpc.ScannerID(s.curRegionScannerID),
-			hrpc.NumberOfRows(s.rpc.NumberOfRows()))
+			hrpc.NumberOfRows(s.rpc.NumberOfRows()),
+			hrpc.Priority(priority),
+		)
 	}
 	if err != nil {
 		return nil, nil, err