Honor etcd legacy v/s new config settings properly (#8510)

This PR also fixes issues related to

- Add proper newline for `mc admin config get` output
  for more than one targets
- Fixes issue of temporary user credentials to have
  consistent output
- Fixes a crash when setting a key with empty values
- Fixes a parsing issue with `mc admin config history`
- Fixes gateway ENV handling for etcd server and gateway

cmd/server-main.go

@@ -235,15 +235,6 @@ func initSafeModeInit(buckets []BucketInfo) (err error) {
 		return err
 	}
 
-	if globalEtcdClient != nil {
-		// ****  WARNING ****
-		// Migrating to encrypted backend on etcd should happen before initialization of
-		// IAM sub-systems, make sure that we do not move the above codeblock elsewhere.
-		if err = migrateIAMConfigsEtcdToEncrypted(globalEtcdClient); err != nil {
-			return fmt.Errorf("Unable to handle encrypted backend for iam and policies: %v", err)
-		}
-	}
-
 	return nil
 }
 
@@ -257,6 +248,15 @@ func initAllSubsystems(buckets []BucketInfo, newObject ObjectLayer) (err error)
 		return fmt.Errorf("Unable to initialize notification target(s) from config: %w", err)
 	}
 
+	if globalEtcdClient != nil {
+		// ****  WARNING ****
+		// Migrating to encrypted backend on etcd should happen before initialization of
+		// IAM sub-systems, make sure that we do not move the above codeblock elsewhere.
+		if err = migrateIAMConfigsEtcdToEncrypted(globalEtcdClient); err != nil {
+			return fmt.Errorf("Unable to handle encrypted backend for iam and policies: %v", err)
+		}
+	}
+
 	if err = globalIAMSys.Init(newObject); err != nil {
 		return fmt.Errorf("Unable to initialize IAM system: %w", err)
 	}