Improve creation of a service for a single domain

Make the most simple case, where the CDN service is only i
fronting a single domain, easier.

Author: carolynvs

src/corelib/ContentDeliveryNetworks/v1/ServiceDefinition.cs

@@ -9,6 +9,18 @@ namespace OpenStack.ContentDeliveryNetworks.v1
     /// <threadsafety static="true" instance="false"/>
     public class ServiceDefinition
     {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ServiceDefinition"/> class.
+        /// </summary>
+        /// <param name="name">The service name.</param>
+        /// <param name="flavorId">The flavor identifier.</param>
+        /// <param name="domain">The service domain.</param>
+        /// <param name="origin">The service asset origin.</param>
+        public ServiceDefinition(string name, string flavorId, string domain, string origin)
+            : this(name, flavorId, new[] {new ServiceDomain(domain)}, new[] {new ServiceOrigin(origin)})
+        {
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="ServiceDefinition"/> class.
         /// </summary>

src/testing/unit/ContentDeliveryNetworks/v1/ServiceTests.cs

@@ -71,16 +71,8 @@ public void CreateService()
                 response.Headers.Location = "http://api.com".AppendPathSegments("services", "service-id").ToUri();
                 httpTest.ResponseQueue.Enqueue(response);
 
-                var service = new ServiceDefinition("service-name", "flavor-id", null, null)
+                var service = new ServiceDefinition("service-name", "flavor-id", "www.example.com", "example.com")
                 {
-                    Domains =
-                    {
-                        new ServiceDomain("example.com")
-                    },
-                    Origins =
-                    {
-                        new ServiceOrigin("assets.example.com")
-                    },
                     Caches =
                     {
                         new ServiceCache("keep-one-day", TimeSpan.FromDays(1))