delete objects based on label

This PR uses the "SelectorFromSet()" function which takes alabel or
selector as an argument returns all the object that uses that label or
selector. Once we get the object that uses a particular label we can
further do the delete operation on them. This is similar to "kubectl
delete <object> --selector=<key>=<value>". Also the label has been
modified from service to io.kompose.service.

pkg/transformer/utils.go

@@ -37,6 +37,7 @@ import (
 )
 
 const letterBytes = "abcdefghijklmnopqrstuvwxyz0123456789"
+const Selector = "io.kompose.service"
 
 // RandStringBytes generates randomly n-character string
 func RandStringBytes(n int) string {
@@ -116,7 +117,7 @@ func isPath(substring string) bool {
 
 // ConfigLabels configures label
 func ConfigLabels(name string) map[string]string {
-	return map[string]string{"service": name}
+	return map[string]string{Selector: name}
 }
 
 // ConfigAnnotations configures annotations