Run control environment variables

[plasorak]

Some of the environmnent variables should really not be set at all in the configuration, and only be set by the run control. So, we should leave them blank, and let the run control decide what they are (for example DUNEDAQ_SESSION).

[alessandrothea]

I suspect we need to be tad more clear about what should and shouldn't be set in configuration. Let's write some specs, shan't we?

[plasorak]

Ok, so here is my proposal:

• In the unified shell (i.e. drunc developper environment), almost all variables can be overriden at boot, but these variables are Session-wide (i.e. you cannot have individual application custom environment).
• There are some dynamic variables that are set by the run control (these variables cannot be overriden by the unified shell):
  • DUNEDAQ_SESSION (and DUNEDAQ_PARTITION): Come from the session name.
  • DUNEDAQ_APPLICATION_NAME: application name.
• There are some variables which the run control sets depending if the configuration (iff the "value" in the configuration is empty), and these could come from the environment:
  • ERSes, TRACEs and logging
  • CONNECTION_PORT: That one is a bit more complicated, because really we want a dynamic port, so the run control tries to find a port free and set that variable.
  • Any other?
• All the other variables are set in configuration.

[plasorak]

Done here: https://github.com/DUNE-DAQ/drunc/pull/250