'User' extension tests fail when invoking user has no groups

[cottsay]

There is a test failure when invoking this package's unit tests from a user that is not explicitly a member of any groups.

=================================== FAILURES ===================================
____________________ UserExtensionTest.test_user_extension _____________________
test/test_extension.py:421: in test_user_extension
    self.assertTrue('usermod -aG' in snippet_result)
E   AssertionError: False is not true
---------- generated xml file: /tmp/ws/test_results/rocker/pytest.xml ----------
=========================== short test summary info ============================
FAILED test/test_extension.py::UserExtensionTest::test_user_extension - Asser...
================= 1 failed, 50 passed, 33 deselected in 1.01s ==================

Repro: https://gist.githubusercontent.com/cottsay/f26a4d7b91ec87a4ef85e98ce9f96bdf/raw/Containerfile

[T-Rajeev30]

Hi , I’d like to take this issue and work on a fix. I’ll post a PR once ready.