Fix the env lookup fallback in rhel_subscribe

The role is looking for the usernames, passwords, etc. first in the
shell environment and then in the Ansible vars.

When the environment is empty, however, the lookup returns an empty
string not an undefined variable, so the `default` fallback is never
used and the ansible variables end up being ignored.

By adding `True` to the end of the filter, it will work with any falsey
value (including an empty string) not just undefined variables.

roles/rhel_subscribe/tasks/main.yml

@@ -4,10 +4,10 @@
 #       to make it able to enable repositories
 
 - set_fact:
-    rhel_subscription_pool: "{{ lookup('env', 'rhel_subscription_pool') | default(rhsub_pool | default('Red Hat OpenShift Container Platform, Premium*')) }}"
-    rhel_subscription_user: "{{ lookup('env', 'rhel_subscription_user') | default(rhsub_user | default(omit, True)) }}"
-    rhel_subscription_pass: "{{ lookup('env', 'rhel_subscription_pass') | default(rhsub_pass | default(omit, True)) }}"
-    rhel_subscription_server: "{{ lookup('env', 'rhel_subscription_server') | default(rhsub_server | default(omit, True)) }}"
+    rhel_subscription_pool: "{{ lookup('env', 'rhel_subscription_pool') | default(rhsub_pool | default('Red Hat OpenShift Container Platform, Premium*'), True) }}"
+    rhel_subscription_user: "{{ lookup('env', 'rhel_subscription_user') | default(rhsub_user | default(omit, True), True) }}"
+    rhel_subscription_pass: "{{ lookup('env', 'rhel_subscription_pass') | default(rhsub_pass | default(omit, True), True) }}"
+    rhel_subscription_server: "{{ lookup('env', 'rhel_subscription_server') | default(rhsub_server | default(omit, True), True) }}"
 
 - fail:
     msg: "This role is only supported for Red Hat hosts"