grub-mkconfig: Honor a symlink when generating configuration by grub-mkconfig

Honor a symlink when generating configuration by grub-mkconfig, so that
the -o option follows it rather than overwriting it with a regular file.

Signed-off-by: Marcel Kolaja <mkolaja@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

util/grub-mkconfig.in

@@ -287,7 +287,8 @@ and /etc/grub.d/* files or please file a bug report with
     exit 1
   else
     # none of the children aborted with error, install the new grub.cfg
-    mv -f ${grub_cfg}.new ${grub_cfg}
+    cat ${grub_cfg}.new > ${grub_cfg}
+    rm -f ${grub_cfg}.new
   fi
 fi