14.04 to 16.04 upgrade failed: ca-certificate and man-db trigger loop

[Jean-Baptiste Lallement]

Upgrade from 14.04 LTS to 16.04 LTS fails with a trigger loop on ca-certificates and man-db

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:0.220.9
ProcVersionSignature: Ubuntu 4.2.0-27.32~14.04.1-generic 4.2.8-ckt1
Uname: Linux 4.2.0-27-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.14
Architecture: amd64
CrashDB: ubuntu
Date: Thu Dec 14 09:43:55 2017
InstallationDate: Installed on 2017-12-14 (0 days ago)
InstallationMedia: Ubuntu-Server 14.04.4 LTS "Trusty Tahr" - Release amd64 (20160217.1)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_US:en
 TERM=linux
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
Symptom: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2017-12-14 (0 days ago)
VarLogDistupgradeAptclonesystemstate.tar.gz: Error: command ['pkexec', 'cat', '/var/log/dist-upgrade/apt-clone_system_state.tar.gz'] failed with exit code 127: Error getting authority: Error initializing authority: Could not connect: No such file or directory