tests: Make effective config check work for container runs

In linux-system-roles/tox-lsr#191 we added
`ansible_become=false` to our container (podman/buildah) inventories.
This disables `become_user`, and thus the test was silently running as
root and thus failing. This isn't important for the stat tests (they are
fine to run as root), but `ssh` must actually run as the desired target
user.

This is just a test, so we can call `su` directly.

Author: martinpitt

tests/tests_user_config.yml

@@ -100,10 +100,9 @@
               - config_mode.stat.mode == '0600'
 
         - name: Test the effective configuration using ssh
-          become: true
-          become_user: "{{ username }}"
-          become_method: "{{ __become_method }}"
-          command: ssh -vvv -G example
+          # don't use become_user, does not work in containers due to
+          # https://github.com/linux-system-roles/tox-lsr/pull/191
+          command: "su -c 'ssh -vvv -G example' {{ username }}"
           register: effective
           when:
             - ansible_facts['distribution'] not in ['CentOS', 'RedHat'] or