Do not delete previous annotation

Currently, if passing another annotations, original previous annotation
will be removed and the passed new annotations will be added.

It may give users some confused that why my previous annotation gone.
So it is better to not delete user's previous annotation when adding new
annotation, but at the same time, need to provide a feature that
support to delete annotation by user via ClI, e.g.
wsk action update hello --del-annotation key1 --del-annotation key2

CLI side needs to support as well

common/scala/src/main/scala/org/apache/openwhisk/core/entity/WhiskAction.scala

@@ -56,7 +56,8 @@ case class WhiskActionPut(exec: Option[Exec] = None,
                           limits: Option[ActionLimitsOption] = None,
                           version: Option[SemVer] = None,
                           publish: Option[Boolean] = None,
-                          annotations: Option[Parameters] = None) {
+                          annotations: Option[Parameters] = None,
+                          delAnnotations: Option[Array[String]] = None) {
 
   protected[core] def replace(exec: Exec) = {
     WhiskActionPut(Some(exec), parameters, limits, version, publish, annotations)
@@ -643,5 +644,5 @@ object ActionLimitsOption extends DefaultJsonProtocol {
 }
 
 object WhiskActionPut extends DefaultJsonProtocol {
-  implicit val serdes = jsonFormat6(WhiskActionPut.apply)
+  implicit val serdes = jsonFormat7(WhiskActionPut.apply)
 }

core/controller/src/main/scala/org/apache/openwhisk/core/controller/Actions.scala

@@ -537,6 +537,14 @@ trait WhiskActionsApi extends WhiskCollectionAPI with PostActionActivation with
 
     val exec = content.exec getOrElse action.exec
 
+    var newAnnotations = action.annotations
+    content.delAnnotations.map { annotationArray =>
+      annotationArray.foreach { annotation =>
+        newAnnotations -= annotation
+      }
+    }
+    newAnnotations = newAnnotations ++ content.annotations
+
     WhiskAction(
       action.namespace,
       action.name,
@@ -545,7 +553,7 @@ trait WhiskActionsApi extends WhiskCollectionAPI with PostActionActivation with
       limits,
       content.version getOrElse action.version.upPatch,
       content.publish getOrElse action.publish,
-      WhiskActionsApi.amendAnnotations(content.annotations getOrElse action.annotations, exec, create = false))
+      WhiskActionsApi.amendAnnotations(newAnnotations, exec, create = false))
       .revision[WhiskAction](action.docinfo.rev)
   }