Bump luatest to 1.0.1-27-g428a2f9

New version includes the following commits related to luatest
functionality:

- Propagate stack trace from `Server:exec()`
- Fix utils.strip_luatest_trace
- Add `assert_items_exclude` matcher
- server: fix assertion error serialization in `exec()`
- Add a long option `--no-capture`
- Make `assert_covers` recursive