Make cgroup enabling idempotent and fix ansible lint checks.

roles/ubuntu/tasks/main.yml

 ---
-- name: Check if cgroups enabled
-  shell: cat /boot/firmware/cmdline.txt | grep cgroup
-  register: cgroup_enabled
-  when: ansible_distribution == 'Ubuntu'
-  # grep will exit with 1 when no results found.
-  # ignore_errors causes the task not to halt play.
-  ignore_errors: true
-
 - name: Enable cgroup via boot commandline if not already enabled
   lineinfile:
     path: /boot/firmware/cmdline.txt
     backrefs: yes
-    regexp: "(.*)$"
+    regexp: '^((?!.*\bcgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory\b).*)$'
     line: '\1 cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory'
   when:
     - ansible_distribution == 'Ubuntu'
-    - cgroup_enabled.stdout == ""
 
-- name: Check if cgroups already running
-  shell: cat /proc/cmdline | grep cgroup
-  register: cgroup_running
+- name: Read /proc/cmdline to check for cgroups already running
+  shell: cat /proc/cmdline
+  register: cmdline
   when:
-    ansible_distribution == 'Ubuntu'
-  # grep will exit with 1 when no results found.
-  # ignore_errors causes the task not to halt play.
-  ignore_errors: true
+    - ansible_distribution == 'Ubuntu'
 
 - name: Reboot to enable cgroups if not already running
   reboot:
   when:
     - ansible_distribution == 'Ubuntu'
-    - cgroup_running.stdout == ""
+    - '"cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory" not in cmdline.stdout'