[dataimport] fix db-namespace default value handling In a fresh new instance, the "db-namespace" option is set as empty by default in the "sources" file. This seems correct but empty string is not a valid pg_schema and actually means that we should use "public"

usr/lib/python2*/*-packages/cubicweb/entities/
usr/lib/python2*/*-packages/cubicweb/ext/
usr/share/cubicweb/cubes/
usr/lib/python2*/*-packages/cubicweb/*.py