[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)

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/share/pyshared/cubicweb/skeleton/debian/rules.tmpl)