[tests/checkintegrity] use the new connection api
* serverctl: the db-check command also uses an internal connection
object, which makes more sense in the context of `checkintegrity`.
* checkintegrity: rename srvcnx to just cnx (a bit because in the near
future, there will be one cnx to rule them all)
usr/lib/PY_VERSION/*-packages/cubicweb/devtools/
usr/lib/PY_VERSION/*-packages/cubicweb/skeleton/
usr/lib/PY_VERSION/*-packages/cubicweb/test
usr/lib/PY_VERSION/*-packages/cubicweb/entities/test
usr/lib/PY_VERSION/*-packages/cubicweb/ext/test
usr/lib/PY_VERSION/*-packages/cubicweb/server/test
usr/lib/PY_VERSION/*-packages/cubicweb/sobjects/test
usr/lib/PY_VERSION/*-packages/cubicweb/hooks/test
usr/lib/PY_VERSION/*-packages/cubicweb/web/test
usr/lib/PY_VERSION/*-packages/cubicweb/etwist/test