auto-upgrade-tester: Add a post-upgrade test to check for obsolete config files

[Jean-Baptiste Lallement]

auto-upgrade-tester: Add a post-upgrade test to check for obsolete config files.
Test fails if the list is not empty.

Script from upgrade-system
  #################################
  ### REMOVING OBSOLETE CONFIGS ###
  #################################
  echo "${BOLD}D) Checking for obsolete configurations:${RESET}"
  ORPHANS=$( dpkg-query -W -f='${Conffiles}\n' | grep obsolete | awk {'print $1'} )
  ##DEPENDS: dpkg (main/required), grep (main/required), mawk (main/required).
  case $ORPHANS in
   "")
    echo "I: No obsolete configuration to purge."
    break
    ;;
   *)
    echo "I: Removing obsolete configurations..."
    unique(){
     dpkg -S $ORPHANS | cut -d ':' -f 1 | uniq
     ##DEPENDS: dpkg (main/required), dpkg (main/required), coreutils (main/required).
     }
    UNIQUE=$( unique )
    NUMBER=$( unique | wc -l )
    echo "I: Number of packages affected: $NUMBER."
    dpkg -S $ORPHANS
    ##DEPENDS: dpkg (main/required).
    echo "${YELLOW}W: BEWARE OF FALSE POSITIVES! DELETE WITH EXTREME CAUTION!${RESET}"
    rm -i $ORPHANS
    ##DEPENDS: coreutils (main/required).
    apt-get $NOTTY --reinstall install ${UNIQUE}
    ##DEPENDS: apt (main/important).
    ### Escape dangerous purges automatically.
    if [ $? != 0 ]
    then
            break
    fi
    ;;
  esac

[Martin-Éric Racine (q-funk)]

Packages spotted by the above recipe need to have a bug filed, requesting that the package calls dpkg-maintscript-helper via debian/*.maintscript content to either move (if there was a rename between versions) or remove the obsolete config, so as to achieve an upgrade that is free of accumulated cruft.

[Jean-Baptiste Lallement (jibel)]

I pushed a script update-manager/AutoUpgradeTester/post_upgrade_tests/test_obsolete_conffiles.py to the auto-upgrade-tester that will be active with next run.