Add missing grub config file update while changing grub configuration for Xen

roles/hypervisor/tasks/xen.yml

@@ -16,6 +16,8 @@
     regexp: '^GRUB_CMDLINE_XEN_DEFAULT='
     insertafter: '^GRUB_CMDLINE_LINUX='
     line: 'GRUB_CMDLINE_XEN_DEFAULT="dom0_mem={{ xendom0_mem  }}M,max:{{ xendom0_mem }}M dom0_max_vcpus=1 dom0_vcpus_pin"'
+  notify:
+    - 'Update GRUB'
   when: with_xen
 
 - name: 'Set Xen hypervisor to boot first'