[dataimport] drop massive store etype to eid index and fix potential problem with is_instance_of relation insertion in case where the class of inserted entity has some (yams) parent.

usr/bin/cubicweb-ctl usr/bin/
usr/lib/python2*/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl