Allow change disk order for grub2

Fix YaST doesn't allow to change disk order when grub2 is choosen as
bootloader (bnc#785569)

src/grub2/dialogs.ycp

@@ -84,6 +84,28 @@ symbol Grub2LoaderDetailsDialog ()
 
 include "bootloader/grub/options.ycp";
 
+/**
+ * Run dialog to adjust installation on i386 and AMD64
+ * @return symbol for wizard sequencer
+ */
+symbol Grub2InstallDetailsDialog () {
+    term contents =  `HBox (`HStretch (), `VBox (
+        `VStretch(),
+        `Frame (_("Disk Order"),"disks_order"),
+        `VStretch()),
+        `HStretch());
+
+    return CWM::ShowAndRun ($[
+        "widget_descr": $[ "disks_order": DisksOrderWidget()],
+        "widget_names": ["disks_order"],
+        "contents": contents,
+        "caption" : _("Disk order settings"),
+        "back_button" : Label::BackButton (),
+        "abort_button" : Label::CancelButton (),
+        "next_button" : Label::OKButton ()
+    ]);
+}
+
 /**
  * Cache for genericWidgets function
  */

src/modules/BootGRUB2.ycp

@@ -208,6 +208,7 @@ global define list<string> Summary () {
 global map<string,symbol()> Dialogs () {
     y2milestone ("Called GRUB2 Dialogs");
     return $[
+	"installation"	: Grub2InstallDetailsDialog,
 	"loader"	: Grub2LoaderDetailsDialog,
     ];
 }

src/routines/global_widgets.ycp

@@ -748,7 +748,7 @@ map TabsDescr () {
 		? `Empty ()
 		: "loader_location",
 	    `VStretch (),
-	    (lt != "grub")
+	    (lt != "grub" && lt != "grub2")
 		? `Empty ()
 		: "inst_details",
 	    `VStretch ()