revise restricted system usernames #2634

[phillxnet]

Update to reflect current OS base (openSUSE), and its users associated with common system services.

Includes

• incidental string.format (and % use) to fstrings - user.py.

N.B. presented as two commits to assist in review & clarify intended functional changes.

Fixes #2634

[phillxnet]

Testing

We already have unit tests in place for the guards/fencing around our restricted user list: we have just revised that list.

Leap 15.5 OS Pre PR

cd /opt/rockstor/src/rockstor
poetry run django-admin test -v 2 -p test_user.py
...
Ran 17 tests in 4.413s

OK

We then modify the following test line:

rockstor-core/src/rockstor/storageadmin/tests/test_user.py

Line 322 in 83030d1

response = self.client.put(f"{self.BASE_URL}/bin", data=data)

To instead reference one of our additional restricted system usernames: i.e. "lp":

    response = self.client.put(f"{self.BASE_URL}/lp", data=data)

and we get our expected failure on this unrestricted system username:

======================================================================
FAIL: test_put_requests (rockstor.storageadmin.tests.test_user.UserTests.test_put_requests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/opt/rockstor/src/rockstor/storageadmin/tests/test_user.py", line 323, in test_put_requests
    self.assertEqual(
AssertionError: 200 != 500 : {'id': None, 'groupname': 'lp', 'managed_user': False, 'has_pincard': False, 'pincard_allowed': 'no', 'username': 'lp', 'uid': 490, 'gid': 487, 'public_key': None, 'shell': '/usr/sbin/nologin', 'homedir': None, 'email': None, 'admin': False, 'user': None, 'group': None, 'smb_shares': []}

----------------------------------------------------------------------
Ran 17 tests in 4.418s

FAILED (failures=1)

I.e. the user modification was allowed (200): AssertionError: 200 != 500

Leap 15.6 OS Post PR (rpm derived install)

Using the same modified test as above: i.e. "bin" to "lp" and we get:

======================================================================
FAIL: test_put_requests (rockstor.storageadmin.tests.test_user.UserTests.test_put_requests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/opt/rockstor/src/rockstor/storageadmin/tests/test_user.py", line 330, in test_put_requests
    self.assertEqual(response.data[0], e_msg)
AssertionError: 'Editing restricted user (lp) is not supported.' != 'Editing restricted user (bin) is not supported.'
- Editing restricted user (lp) is not supported.
?                          ^^
+ Editing restricted user (bin) is not supported.
?                          ^^^


----------------------------------------------------------------------
Ran 17 tests in 4.551s

FAILED (failures=1)

Confirming that our newly added "lp" user is now treated as a restricted user: as "bin" was already.