Change VNC settings via environment variable

[darkdragon-001]

• Move password creation from Dockerfile to newly created entrypoint.sh.
• Use -geometry (resolution) and -depth (color depth) with environment variable in tigervnc.service (NOTE environment variables need to be handled specifically in systemd services)

[mviereck]

environment variables need to be handled specifically in systemd services

You can specify environment variables for all systemd services in /etc/systemd/system.conf.d/myenvvars.conf. x11docker creates such a file and shares it with the container. Sample file content:

[Manager]
DefaultEnvironment=container=docker XAUTHORITY=/x11docker/Xclientcookie DISPLAY=:252 XDG_RUNTIME_DIR=/tmp/XDG_RUNTIME_DIR 

All variables must be in one line. I don't understand this entirely, but it works.

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Edit: systemd clears all environment variables set with --env. Alternatively, the image could be set up with runit, dbus and elogind to allow --env again. runit replaces systemd and elogind replaces systemd-logind. Basically Gnome 3 needs a logind service and DBus.

Edit2: Thinking again about this: Maybe not a great idea. elogind needs a cgroup that needs either to be mounted on host or created in container with capability SYS_ADMIN.