Add support to set backups with tag, which overwrites existing

Notice, this will overwrite existing tag if it exists, use with caution

pkg/cain/nodetool.go

@@ -13,10 +13,14 @@ import (
 // TakeSnapshots takes a snapshot using nodetool in all pods in parallel
 func TakeSnapshots(iClient interface{}, pods []string, namespace, container, keyspace string, username string, password string, tag string) string {
 	k8sClient := iClient.(*skbn.K8sClient)
+
+	// get current time as tag
 	realtag := utils.GetTimeStamp()
-	if len(tag) == 0 {
+	// set custom tag if provided
+	if len(tag) != 0 {
 		realtag = tag
 	}
+
 	bwgSize := len(pods)
 	bwg := utils.NewBoundedWaitGroup(bwgSize)
 	for _, pod := range pods {