add select_existing to plugindata for iscsi(direct)

this will be used in the gui, for determining if we need to select
something from the storage when using for an image

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

PVE/Storage/ISCSIDirectPlugin.pm

@@ -56,7 +56,8 @@ sub type {
 
 sub plugindata {
     return {
-        content => [ {images => 1, none => 1}, { images => 1 }],
+	content => [ {images => 1, none => 1}, { images => 1 }],
+	select_existing => 1,
     };
 }
 

PVE/Storage/ISCSIPlugin.pm

@@ -237,6 +237,7 @@ sub type {
 sub plugindata {
     return {
 	content => [ {images => 1, none => 1}, { images => 1 }],
+	select_existing => 1,
     };
 }