Apply lib2to3.fixes.fix_asserts

Ran https://github.com/python/cpython/blob/3.7/Lib/lib2to3/fixes/fix_asserts.py after adding the missing methods (assertRegex and assertRaisesRegex) on ERP5TypeTestCase.

Also ran a custom fixer rewriting

self.assertTrue(a in b)

into

self.assertIn(a, b)