cubicweb #2710515 dbapi: when get_repository crashes show the full backtrace [done]

in the logs at least, instead of just reraising ConnectionError with the latest message

prioritynormal
typebug
done in3.16.1
load0.100
load left0.000
closed by#d47089677d44 [dbapi] Stop shadowing exceptions in get_repository() (closes #2710515)