[tests/repository] use the new connection api (part 2/2)
Some notes:
* module imports cleanup
* the unimplemented `test_transaction_interleaved` is wiped
ifnotrql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',ask_confirm=False):rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',ask_confirm=False)