users: Delete or move home folder when user is deleted or renamed

Also:

• Add a simple username validation to the privileged actions.
• Functional tests: Create a fixture to login as an admin before every test.
• Functional tests: Add a test to check that SSH passwordless login works after user is renamed to validate correct SSH related path permissions.
• Privileged tests: Add test_ prefix to the generated random string which makes easier to check and cleanup created home folders.
• Minor quote fixes.

Tests performed in stable and testing containers:

• Run all the users module tests twice, no failures in tests.

Closes #2451 (closed).

Signed-off-by: Veiko Aasa veiko17@disroot.org