[repository,tests] use the new connection api (part 1/2)
`add_info` should not play with the cnxset nor the mode.
Static analysis showed that:
* add_info is an internal api called with a non-none cnx.cnxset and
also in write mode
* only the altered test violated this assumption, which is now
somewhat documented
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html