QMT to Pytest migration in Rec

Ports the tests in Rec from QMTest to Pytest. Following migration in gaudi/Gaudi!1605 (merged) and in LHCb!4773 (merged).

The tests are based on LHCbExeTest class. The exclusive preprocessor for Rec was added in RecTesting/preprocessors.py.

All tests have been ported to Pytest.

Requires LHCb!4959 (merged) and gaudi/Gaudi!1703 (merged) and could be improved with features from the patch LHCb!5004 (merged).

Edit: requires LHCb!5106