always use real devices for generic mbr (found during manual testing)

src/lib/bootloader/mbr_update.rb

@@ -139,6 +139,10 @@ def disks_to_rewrite
       ret = [mbr_disk]
       # Add to disks only if part of raid on base devices lives on mbr_disk
       ret.concat(mbrs) if mbrs.include?(mbr_disk)
+      # get only real disks
+      ret = ret.each_with_object([]) do |disk, res|
+        res.concat(::Bootloader::Stage1Device.new(disk).real_devices)
+      end
 
       ret.uniq
     end

test/mbr_update_test.rb

@@ -119,6 +119,20 @@ def stage1(devices: [], activate: false, generic_mbr: false)
         subject.run(stage1(generic_mbr: true))
       end
 
+      it "always uses real devices" do
+        allow(Yast::BootStorage).to receive(:mbr_disk)
+          .and_return("/dev/md0")
+
+        allow(::Bootloader::Stage1Device).to receive(:new).with("/dev/md0")
+          .and_return(double(real_devices: ["/dev/sda1", "/dev/sdb1"]))
+        expect(Yast::Execute).to receive(:on_target).at_least(:twice) do |*args|
+          next nil unless args.first =~ /dd/
+          next nil unless args.include?("of=/dev/sdb")
+          expect(args).to be_include("of=/dev/sda")
+        end
+        subject.run(stage1(generic_mbr: true))
+      end
+
       it "install syslinux if non on initial stage" do
         allow(Yast::Stage).to receive(:initial).and_return(false)
         expect(Yast::PackageSystem).to receive(:Install).with("syslinux")