RTCDS needs to conditionally add systemd environment variables

from /etc/advligorts/systemd_env*

These can only be in the form "VAR=VALUE"

Currently the rtcds start script reads these files in as if they were bash files, but they override any variable in the environment. That's not acceptable. User environment should take precedence.

The only solution I can think of is to parse these files in RTCDS.