[tests/repository] use the new connection api (part 2/2) Some notes: * module imports cleanup * the unimplemented `test_transaction_interleaved` is wiped

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