Handle kernel options for Grub 2 when using Xen.

When you are using the Xen virtualization hypervisor, you need to
set a different variable, GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT, in
/etc/default/grub to pass kernel options to the Dom0 Linux kernel,
instead of GRUB_CMDLINE_LINUX when not using Xen.  Detect when Xen
Dom0 is used in bootloader::grub2::kernel_option and do the right
thing.

manifests/grub2/kernel_option.pp

@@ -10,9 +10,13 @@ define bootloader::grub2::kernel_option($ensure, $value)
     include bootloader::grub2::rebuild_grub_cfg
 
     $grub_defaults_file = '/etc/default/grub'
+    $cfgparam = $::virtual ? {
+	'xen0'  => 'GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT',
+	default => 'GRUB_CMDLINE_LINUX',
+    }
     $qname = regexp_quote($name)
     # Augeas path expression to find nodes for the kernel parameter
-    $pathexpr = "GRUB_CMDLINE_LINUX/value[. =~ regexp('${qname}(=.*)?')]"
+    $pathexpr = "${cfgparam}/value[. =~ regexp('${qname}(=.*)?')]"
 
     if ($ensure == 'absent')
     {