[test] fix tests when executed in an apycot environment ie. when tests are executed from sources towards an installed apycot. The fix consist mainly in "moving" the input_path function from testutils.py (which is part of the installed modules) into unittest_checkers.py so we are sure we look for test data files relatively to the test directory (and not the location of the installation).

"""cubicweb-apycot"""
from cubicweb.schema import ETYPE_NAME_MAP
ETYPE_NAME_MAP['TestConfigGroup'] = 'TestConfig'