Added health check for connections from SSP

[eidekrist]

This fixes #336 with better handling of invalid connections specified in SystemStructure.ssd.

The direct map lookup (i.e. val = map[key]) used in the previous solution could give some funky results, and might even create a valid but unintended connection.

I added a try-catch around the call to execution::add_connection() creating a more detailed and hopefully understandable error message. I'm not sure if this is how we want to do things, so input is welcome.

[markaren]

I tested with invalid endElement and endConnector. Did not notice a difference?

[eidekrist]

I tested with invalid endElement and endConnector. Did not notice a difference?

As in nothing happened, or exception is thrown both for old and new solution?

A test case could be the first connection for cse-demos/house:

<ssd:Connection startElement="OuterWall1" startConnector="h_wall" endElement="Room1" endConnector="h_OuterWall"/>

When specifying wrong/nonexistent startElement, the old solution would give you a default entry in the slaves map, resulting in a connection from Clock:Clock to Room1:h_Outerwall. The proposed changes will throw an exception.

[markaren]

https://gist.github.com/markaren/bb97bd40e2bce6ca2be9775001f0205c

Thats the output from the debug build. As before the simulations just silently fails and hangs at the end. No exceptions. No error message.

[markaren]

I removed use of fmu-proxy FMUs, just to see if that had something to do with it. But same result.

[markaren]

Ok, I guess it has to do with the FMUs used by the gunnerus-case. They do not shutdown properly, so the application hangs and the user never gets the error message..

Because I get the correct error handling when loading the demo case in the data folder.

[kyllingstad]

Approved in mob session.