speed up startup sequence for all operations (#14148)

This speed-up is intended for faster startup times
for almost all MinIO operations. Changes here are

- Drives are not re-read for 'format.json' on a regular
  basis once read during init is remembered and refreshed
  at 5 second intervals.

- Do not do O_DIRECT tests on drives with existing 'format.json'
  only fresh setups need this check.

- Parallelize initializing erasureSets for multiple sets.

- Avoid re-reading format.json when migrating 'format.json'
  from really old V1->V2->V3

- Keep a copy of local drives for any given server in memory
  for a quick lookup.

cmd/config.go

@@ -35,8 +35,8 @@ import (
 
 const (
 	minioConfigPrefix = "config"
-
-	kvPrefix = ".kv"
+	minioConfigBucket = minioMetaBucket + SlashSeparator + minioConfigPrefix
+	kvPrefix          = ".kv"
 
 	// Captures all the previous SetKV operations and allows rollback.
 	minioConfigHistoryPrefix = minioConfigPrefix + "/history"