Refactor running unit tests

[rvs]

Unit tests need to be put into a separate check in the circle pipeline and we also need to make sure make test target returns non-0 exit code if tests fail

[dave-tucker]

It looks like this is already a seperate check. For example, on #391, the test job == unit tests.

[dave-tucker]

I've also verified that the exit code does indeed propagate correctly, although there is no feedback as to which test failed without reading the Junit report. I'll open an (optional) PR to address that but based on the description of the issue I think this can be closed.

[milan-zededa]

Done by @dave-tucker