Move clientname default value to configuration manager.

StackExchange.Redis/StackExchange/Redis/ConfigurationOptions.cs

@@ -162,7 +162,7 @@ public static string TryNormalize(string value)
         /// <summary>
         /// The client name to use for all connections
         /// </summary>
-        public string ClientName { get { return clientName ?? (clientName = AzureRoleInstanceId); } set { clientName = value; } }
+        public string ClientName { get { return clientName ?? (clientName = (AzureRoleInstanceId != null ? AzureRoleInstanceId : Environment.GetEnvironmentVariable("ComputerName"))); } set { clientName = value; } }
 
         /// <summary>
         /// The number of times to repeat the initial connect cycle if no servers respond promptly

StackExchange.Redis/StackExchange/Redis/ConnectionMultiplexer.cs

@@ -91,7 +91,7 @@ public ServerCounters GetCounters()
         /// <summary>
         /// Gets the client-name that will be used on all new connections
         /// </summary>
-        public string ClientName => configuration.ClientName ?? Environment.GetEnvironmentVariable("ComputerName");
+        public string ClientName => configuration.ClientName;
 
         /// <summary>
         /// Gets the configuration of the connection