Add "None" value for Disk Caching.

Author: hyonholee

src/ResourceManager/Compute/Commands.Compute/Common/ConstantStringTypes.cs

@@ -47,6 +47,7 @@ public static class ValidateSetValues
     {
         public const string ReadOnly = "ReadOnly";
         public const string ReadWrite = "ReadWrite";
+        public const string None = "None";
     }
 
     public static class ProfileNouns

src/ResourceManager/Compute/Commands.Compute/VirtualMachine/Config/AddAzureVMDataDiskCommand.cs

@@ -60,7 +60,7 @@ public class AddAzureVMDataDiskCommand : Microsoft.Azure.Commands.ResourceManage
             ValueFromPipelineByPropertyName = true,
             HelpMessage = HelpMessages.VMDataDiskCaching)]
         [ValidateNotNullOrEmpty]
-        [ValidateSet(ValidateSetValues.ReadOnly, ValidateSetValues.ReadWrite)]
+        [ValidateSet(ValidateSetValues.ReadOnly, ValidateSetValues.ReadWrite, ValidateSetValues.None)]
         public string Caching { get; set; }
 
         [Parameter(

src/ResourceManager/Compute/Commands.Compute/VirtualMachine/Config/SetAzureVMDataDiskCommand.cs

@@ -68,7 +68,7 @@ public class SetAzureVMDataDiskCommand : Microsoft.Azure.Commands.ResourceManage
             ValueFromPipelineByPropertyName = true,
             HelpMessage = HelpMessages.VMDataDiskCaching)]
         [ValidateNotNullOrEmpty]
-        [ValidateSet(ValidateSetValues.ReadOnly, ValidateSetValues.ReadWrite)]
+        [ValidateSet(ValidateSetValues.ReadOnly, ValidateSetValues.ReadWrite, ValidateSetValues.None)]
         public string Caching { get; set; }
 
         [Parameter(

src/ResourceManager/Compute/Commands.Compute/VirtualMachine/Config/SetAzureVMOSDiskCommand.cs

@@ -65,7 +65,7 @@ public class SetAzureVMOSDiskCommand : Microsoft.Azure.Commands.ResourceManager.
             ValueFromPipelineByPropertyName = true,
             HelpMessage = HelpMessages.VMOSDiskCaching)]
         [ValidateNotNullOrEmpty]
-        [ValidateSet(ValidateSetValues.ReadOnly, ValidateSetValues.ReadWrite)]
+        [ValidateSet(ValidateSetValues.ReadOnly, ValidateSetValues.ReadWrite, ValidateSetValues.None)]
         public string Caching { get; set; }
 
         [Alias("SourceImage")]