Ensure Imp tests have realistic initial SPO thresholds

[teodanciu]

At the moment, SPO thresholds are not being set in the conway Imp initialization, so this means all SPO thresholds are set to 0 .
Some tests that need to check SPO behavior is setting them to something else.

But it would be more realistic to have them set to non-zero for all tests, so that we are always aware in tests of the SPOs (and if necessary, set them explicitly, in each case, to 0 if necessary).