tests: Use monkeypatch in tests to guarantee cleanup
tests: Use monkeypatch in tests to guarantee cleanup

Before, in test_with_reloader(), we set
`Reloader.watch = fake_watch` directly,
and then never restored it back to the original implementation. Fix
this, and while we're at it make the other
tests cleaner by using pytest's
monkeypatch feature, which guarantees
cleanup after each test.

Fix/improve some variable names while we're at it.

Ceasar/staticjinja,Ceasar/staticjinja