add configurable delta for skipping shards (#13967)

This PR is an attempt to make this configurable
as not all situations have same level of tolerable
delta, i.e disks are replaced days apart or even
hours.

There is also a possibility that nodes have drifted
in time, when NTP is not configured on the system.

cmd/common-main.go

@@ -67,6 +67,7 @@ import (
 
 // serverDebugLog will enable debug printing
 var serverDebugLog = env.Get("_MINIO_SERVER_DEBUG", config.EnableOff) == config.EnableOn
+var shardDiskTimeDelta time.Duration
 var defaultAWSCredProvider []credentials.Provider
 
 func init() {
@@ -136,6 +137,12 @@ func init() {
 		},
 	}
 
+	var err error
+	shardDiskTimeDelta, err = time.ParseDuration(env.Get("_MINIO_SHARD_DISKTIME_DELTA", "1m"))
+	if err != nil {
+		shardDiskTimeDelta = 1 * time.Minute
+	}
+
 	// All minio-go API operations shall be performed only once,
 	// another way to look at this is we are turning off retries.
 	minio.MaxRetry = 1