Failed to connect to socket /com/ubuntu/upstart: Connection refused

.xsession-errors has many entries like:

upstart: upstart-event-bridge main process (1511) terminated with status 1
upstart: upstart-event-bridge respawning too fast, stopped

The terminal output is :
 sudo status upstart-event-bridge
[sudo] password for oem:
status: Unable to connect to Upstart: Failed to connect to socket /com/ubuntu/upstart: Connection refused

ls -l /usr/share/upstart/sessions/upstart-event-bridge.conf
-rw-r--r-- 1 root root 385 may 18 12:21 /usr/share/upstart/sessions/upstart-event-bridge.conf

This issue has been reported many times by the past, and already fixed:
 https://bugs.launchpad.net/ubuntu/+source/upstart/+bug/901038/comments/14
https://bugs.launchpad.net/ubuntu/+source/upstart/+bug/1449765

Some workarounds also have been proposed, like:
dpkg-divert --local --rename --add /sbin/initctl
ln -s /bin/true /sbin/initctl

But with the recent ubuntu realeases systemd is now doing more & more jobs previously done by upstart. So the solutions of the past might not be the best choice nowadays.

And the http://upstart.ubuntu.com/cookbook/ seems outdated as it does not consider the systemd existence.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: upstart 1.13.2-0ubuntu14
ProcVersionSignature: Ubuntu 4.2.0-10.10-generic 4.2.0
Uname: Linux 4.2.0-10-generic i686
NonfreeKernelModules: nvidia
ApportVersion: 2.18.1-0ubuntu1
Architecture: i386
CurrentDesktop: GNOME
Date: Sun Sep 13 11:06:23 2015
ProcKernelCmdline: BOOT_IMAGE=/boot/vmlinuz-4.2.0-10-generic root=UUID=7b1f4a51-558f-468f-85e0-f815d2f791e1 ro intel_iommu=on
SourcePackage: upstart
UpgradeStatus: No upgrade log present (probably fresh install)
UpstartBugCategory: System
UpstartRunningSessionVersion: upstart 1.13.2
UpstartRunningSystemJobs:
 Error: command ['initctl', '--system', 'list'] failed with exit code 1: initctl: Name "com.ubuntu.Upstart" does not exist
UpstartRunningSystemVersion: Error: command ['initctl', '--system', 'version'] failed with exit code 1: initctl: Name "com.ubuntu.Upstart" does not exist
modified.conffile..etc.apparmor.d.usr.sbin.rsyslogd: [modified]
modified.conffile..etc.at.deny: [inaccessible: [Errno 13] Permission denied: '/etc/at.deny']
modified.conffile..etc.init.plymouth.upstart.bridge.conf: [modified]
mtime.conffile..etc.apparmor.d.usr.sbin.rsyslogd: 2014-12-16T17:58:59.466381
mtime.conffile..etc.init.plymouth.upstart.bridge.conf: 2015-02-21T17:45:18.251803