This argument print unit dependencies as a list instead of a tree and
avoid showing sometimes colored dot. This dots are displayed to identify
failed units but messed with the awk command, so this failed unit is
never seen. With this --plain argument, dots are not displayed anymore.
These services are running fine, so the extinfo would mostly just clutter
the webui while making the extinfo of relevant (i.e. down) services
harder to find.
