Fix an issue of cannot indicate starttime and expirytime in New-AzureStorageAccountSAS cmdlet.

Author: EmmaZhu

src/Common/Storage/Commands.Storage/Common/Cmdlet/NewAzureStorageAccountSasToken.cs

@@ -39,10 +39,10 @@ public class NewAzureStorageAccountSasTokenCommand : StorageCloudBlobCmdletBase
         public string IPAddressOrRange { get; set; }
 
         [Parameter(Mandatory = false, HelpMessage = "Start Time")]
-        DateTime? StartTime { get; set; }
+        public DateTime? StartTime { get; set; }
 
         [Parameter(Mandatory = false, HelpMessage = "Expiry Time")]
-        DateTime? ExpiryTime { get; set; }
+        public DateTime? ExpiryTime { get; set; }
 
         /// <summary>
         /// Initializes a new instance of the NewAzureStorageAccountSasTokenCommand class.