software/theia: Fix slapos env discrepancy
Fix the environment variables discrepancy between the interactive theia shell and the supervisord services causing slapos node software launched in one context to conflict with previous runs in the other context.
Explanation:
In theia, the user can either manually launch slapos node software from the command line in the interactive shell, or as a supervisord service (e.g. as a periodic background task).
The environment discrepancy between the two contexts caused an invocation of slapos node software in one context to rebuild everything (reboostrap) even if the software had all already been installed from the other context.
ALSO: improve a theia test along the way.