Add default for undefined variables to false

* Add default filter to set `accounts_polyinstantiated_tmp` and
  `accounts_polyinstantiated_var_tmp` to false if not defined

Author: asser

linux_os/guide/system/permissions/partitions/mount_option_nodev_nonroot_local_partitions/ansible/shared.yml

@@ -44,8 +44,8 @@
     - "item.options is not search('nodev')"
     - "item.fstype not in excluded_fstypes"
     # Attempting to change polyinstantiated mounts for /tmp and /var/tmp, if present, will fail
-    - "not accounts_polyinstantiated_var_tmp or item.mount != '/var/tmp/tmp-inst'"
-    - "not accounts_polyinstantiated_tmp or item.mount != '/tmp/tmp-inst'"
+    - "not accounts_polyinstantiated_var_tmp | default(false) or item.mount != '/var/tmp/tmp-inst'"
+    - "not accounts_polyinstantiated_tmp | default(false) or item.mount != '/tmp/tmp-inst'"
   with_items:
     - "{{ ansible_facts.mounts }}"