Trust packages for whether reboot is necessary

Installing a kernel package on Ubuntu creates a
/var/run/reboot-required file. Key off its existence instead of trying
to figure out ourselves whether to reboot.

The `removes' argument to `command' handles conditioning the reboot on
whether the file exists.

For a vagrant instance, fire a `vagrant reload' after rebooting from
on the machine so we still get the setup `vagrant up' does.

tasks/main.yml

@@ -45,10 +45,6 @@
   register: cgroup_lite_result
   when: ansible_distribution_version == '13.10'
 
-- name: Is reboot necessary?
-  set_fact:
-    reboot_needed: "{{(kernel_result or cgroup_lite_result or {'changed': False}) | changed}}"
-
 - include: reboot-and-wait.yml
 
 # Newer versions of Docker no longer require apparmor, but it seems like a good thing to have.

tasks/reboot-and-wait.yml

@@ -6,17 +6,13 @@
 
 - name: Reboot instance
   command: /sbin/shutdown -r now
+  args:
+    removes: /var/run/reboot-required
   register: reboot_result
-  when:
-    - reboot_needed
-    - not is_vagrant
 
-- name: Reboot vagrant instance
+- name: Reload vagrant instance
   local_action: command vagrant reload "{{inventory_hostname}}"
-  register: reboot_result
-  when:
-    - reboot_needed
-    - is_vagrant
+  when: reboot_result|changed and is_vagrant
   become: false
 
 - name: Wait for instance to come online
@@ -29,4 +25,3 @@
     state: started
   when: reboot_result|changed
   become: false
-