ssh-agent support fails to open pinentry (missing DBUS_SESSION_BUS_ADDRESS)

[Chris Halse Rogers]

I use an authentication subkey of my GPG key on my Yubikey hardware token as my SSH key. This works fine in Bionic with gpg-agent's ssh-agent support, and, until a couple of weeks ago, worked fine on Cosmic.

Now it fails (GPG *signing* works fine), complaining about “invalid ioctl for device” in the journalctl logs.

This turns out to be an environment issue - running
```
systemctl --user set-environment DBUS_SESSION_BUS_ADDRESS=$DBUS_SESSION_BUS_ADDRESS
systemctl --user restart gpg-agent
```
results in a working pinentry popup, and successful authentication for SSH sessions.

Either gnupg has changed to require this environment for its ssh-agent support, or systemd has stopped exporting this environment variable into user session units.

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: gpg-agent 2.2.8-1ubuntu1
ProcVersionSignature: Ubuntu 4.16.0+bcachefs.git20180614.0eb4ad1d-1-generic 4.16.0
Uname: Linux 4.16.0+bcachefs.git20180614.0eb4ad1d-1-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.10-0ubuntu7
Architecture: amd64
CurrentDesktop: communitheme:ubuntu:GNOME
Date: Thu Aug 16 17:57:31 2018
SourcePackage: gnupg2
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.