Add DBUS_SESSION_BUS_ADDRESS to env_keep (Fixes #358)

[a-k-g]

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[hnryjms]

What if we change the ENV line in the Dockerfile for Chrome to instead write the variable to Ubuntu's /etc/environment path? I haven't tried this in the Selenium docker machine to confirm it fixes the issue, but when running a simple ubuntu:16.04 box (the origin of Selenium base), this diff adds environment variable changes when running sudo -E -i -u [username] env as well as regular env

USER seluser
# Following line fixes
# https://github.com/SeleniumHQ/docker-selenium/issues/87
- ENV DBUS_SESSION_BUS_ADDRESS=/dev/null
+ RUN echo "DBUS_SESSION_BUS_ADDRESS=/dev/null" >> /etc/environment

[a-k-g]

That should do it as well. I don't have a preference for either approach. I can update the PR if that's a more desirable approach.

[ddavison]

is this succeeded by #386 ? can we close this one in favor of that?

[a-k-g]

Yeah, sure.