rhsm modules: cleanly fail when not run as root (#6211)

subscription-manager on RHEL installs a symlink in /usr/bin to
console-helper (part of usermode), which triggers an interactive prompt
for root credentials when run as user. It seems that console-helper
does not handle well non-interactive contexts (e.g. without a TTY for
input), and thus it will hang waiting for input when run as user in an
Ansible task.

Since subscription-manager requires root already anyway (and it will
fail when explicitly run as user), then apply the same logic locally on
all the modules that interact with it: redhat_subscription,
rhsm_release, and rhsm_repository.

plugins/modules/rhsm_release.py

@@ -18,6 +18,8 @@ notes:
   - This module will fail on an unregistered system.
     Use the C(redhat_subscription) module to register a system
     prior to setting the RHSM release.
+  - It is possible to interact with C(subscription-manager) only as root,
+    so root permissions are required to successfully run this module.
 requirements:
   - Red Hat Enterprise Linux 6+ with subscription-manager installed
 extends_documentation_fragment:
@@ -63,6 +65,7 @@ current_release:
 
 from ansible.module_utils.basic import AnsibleModule
 
+import os
 import re
 
 # Matches release-like values such as 7.2, 5.10, 6Server, 8
@@ -109,6 +112,11 @@ def main():
         supports_check_mode=True
     )
 
+    if os.getuid() != 0:
+        module.fail_json(
+            msg="Interacting with subscription-manager requires root permissions ('become: true')"
+        )
+
     target_release = module.params['release']
 
     # sanity check: the target release at least looks like a valid release