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/format-erasure_test.go

@@ -132,11 +132,12 @@ func TestFormatErasureMigrate(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if err = formatErasureMigrate(rootPath); err != nil {
+	formatData, _, err := formatErasureMigrate(rootPath)
+	if err != nil {
 		t.Fatal(err)
 	}
 
-	migratedVersion, err := formatGetBackendErasureVersion(pathJoin(rootPath, minioMetaBucket, formatConfigFile))
+	migratedVersion, err := formatGetBackendErasureVersion(formatData)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -179,7 +180,7 @@ func TestFormatErasureMigrate(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if err = formatErasureMigrate(rootPath); err == nil {
+	if _, _, err = formatErasureMigrate(rootPath); err == nil {
 		t.Fatal("Expected to fail with unexpected backend format")
 	}
 
@@ -199,7 +200,7 @@ func TestFormatErasureMigrate(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if err = formatErasureMigrate(rootPath); err == nil {
+	if _, _, err = formatErasureMigrate(rootPath); err == nil {
 		t.Fatal("Expected to fail with unexpected backend format version number")
 	}
 }