Avoid using fastjson parser pool, move back to jsoniter (#8190)

It looks like from implementation point of view fastjson
parser pool doesn't behave the same way as expected
when dealing many `xl.json` from multiple disks.

The fastjson parser pool usage ends up returning incorrect
xl.json entries for checksums, with references pointing
to older entries. This led to the subtle bug where checksum
info is duplicated from a previous xl.json read of a different
file from different disk.

cmd/policy.go

@@ -163,20 +163,25 @@ func (sys *PolicySys) Init(objAPI ObjectLayer) error {
 	// the following reasons:
 	//  - Read quorum is lost just after the initialization
 	//    of the object layer.
-	for range newRetryTimerSimple(doneCh) {
-		// Load PolicySys once during boot.
-		if err := sys.refresh(objAPI); err != nil {
-			if err == errDiskNotFound ||
-				strings.Contains(err.Error(), InsufficientReadQuorum{}.Error()) ||
-				strings.Contains(err.Error(), InsufficientWriteQuorum{}.Error()) {
-				logger.Info("Waiting for policy subsystem to be initialized..")
-				continue
+	retryTimerCh := newRetryTimerSimple(doneCh)
+	for {
+		select {
+		case <-retryTimerCh:
+			// Load PolicySys once during boot.
+			if err := sys.refresh(objAPI); err != nil {
+				if err == errDiskNotFound ||
+					strings.Contains(err.Error(), InsufficientReadQuorum{}.Error()) ||
+					strings.Contains(err.Error(), InsufficientWriteQuorum{}.Error()) {
+					logger.Info("Waiting for policy subsystem to be initialized..")
+					continue
+				}
+				return err
 			}
-			return err
+			return nil
+		case <-globalOSSignalCh:
+			return fmt.Errorf("Initializing Policy sub-system gracefully stopped")
 		}
-		break
 	}
-	return nil
 }
 
 // NewPolicySys - creates new policy system.