[core][mback_norm] fix configuration read from mback_norm

4 jobs for larch_usability in 4 minutes and 35 seconds
Status Job ID Name Coverage
  Test
passed #45470
test:python3.5-stretch-pyqt5_larch

00:03:55

passed #45469
test:python3.5-stretch-pyqt5_pymca

00:04:24

passed #45471
test:python3.5-stretch-pyqt5_pymca_larch

00:04:35

passed #45472
test:test-xas-tutorials_pymca

00:03:14