[dataimport] add tests for SQLGenObjectStore (closes #9177565)
Stolen from the massive import store, with the irrelevant bits removed.
Remove redundant tests from test_pgstore.py.
usr/lib/python2*/*-packages/cubicweb/dataimport/
usr/lib/python2*/*-packages/cubicweb/server/
usr/lib/python2*/*-packages/cubicweb/hooks/
usr/lib/python2*/*-packages/cubicweb/sobjects/
usr/lib/python2*/*-packages/cubicweb/schemas/
usr/share/cubicweb/migration/