Adjust route options behaviour for manifest push

Overwrite behaviour for route options is now fixed and tested:
Existing options are not modified if options is nil, {} or not provided
A single option (e.g. loadbalancing-algorithm) can be removed by setting its value to nil

app/actions/route_update.rb

@@ -4,13 +4,17 @@ def update(route:, message:)
       Route.db.transaction do
         if message.requested?(:options)
           route.options = if message.options.nil?
-                            nil
+                            route.options
                           elsif route.options.nil?
                             message.options
                           else
                             route.options.merge(message.options)
                           end
         end
+
+        # remove nil values from options
+        route.options = route.options.compact if route.options
+
         route.save
         MetadataUpdate.update(route, message)
       end

lib/cloud_controller/app_manifest/manifest_route.rb

@@ -19,7 +19,7 @@ def self.parse(route, options=nil)
 
       if options
         attrs[:options] = {}
-        attrs[:options][:lb_algo] = options[:'loadbalancing-algorithm'] if options[:'loadbalancing-algorithm']
+        attrs[:options][:lb_algo] = options[:'loadbalancing-algorithm'] if options.key?(:'loadbalancing-algorithm')
       end
 
       ManifestRoute.new(attrs)