Expose parent resource reference internally

Allow inheriting classes, such as a vendor extension, and us internally
to set the parent resource reference. Anyone but the consuming
user. It's not needed to access for testing, if properly using HttpTest,
as the classes will all be deserialized and initialized by the ApiBuilder.

Author: carolynvs

src/corelib/Compute/v2_1/ImageMetadata.cs

@@ -23,7 +23,8 @@ public class ImageMetadata : Dictionary<string, string>, IHaveExtraData, IChildR
 
         object IServiceResource.Owner { get; set; }
 
-        internal void SetParent(ImageReference parent)
+        /// <summary />
+        protected internal void SetParent(ImageReference parent)
         {
             Image = parent;
         }

src/corelib/Compute/v2_1/Server.cs

@@ -190,7 +190,7 @@ public string AdminPassword
         [OnDeserialized]
         private void OnDeserializedMethod(StreamingContext context)
         {
-            foreach (IChildResource volume in AttachedVolumes)
+            foreach (var volume in AttachedVolumes)
             {
                 volume.SetParent(this);
             }

src/corelib/Compute/v2_1/ServerVolumeReference.cs

@@ -22,7 +22,8 @@ public class ServerVolumeReference : IHaveExtraData, IChildResource
 
         object IServiceResource.Owner { get; set; }
 
-        internal void SetParent(ServerReference parent)
+        /// <summary />
+        protected internal void SetParent(ServerReference parent)
         {
             ServerRef = parent;
         }