Add helper class for rebuilding Grub 2 config file.

Grub 2 builds its config file (/boot/grub2/grub.cfg) from templates
in /etc/grub.d, and settings in /etc/default/grub, and it needs to
be regenerated every time you change those templates or settings (or
when you install a new kernel, et.c).  This adds a class for doing
so, bootloader::grub2::rebuild_grub_cfg.

manifests/grub2/rebuild_grub_cfg.pp

+# Copyright © 2017   Thomas Bellman, Linköping, Sweden
+# Licensed under the GNU LGPL v3+; see the README file for more information.
+
+
+/*
+ * Rebuild the Grub 2.x config file.
+ */
+class bootloader::grub2::rebuild_grub_cfg
+{
+    exec {
+	'bootloader::grub2::rebuild_grub_cfg':
+	    command => 'grub2-mkconfig -o /boot/grub2/grub.cfg',
+	    path => ['/bin', '/usr/bin', '/sbin', '/usr/sbin'],
+	    refreshonly => true;
+    }
+}