[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
addressbook
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blog
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comment
company
email
file
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i18ncontent
keyword
link
mailinglist
person
tag
timeseries
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