`test_minimum_service_factor` marked as xfail

[tsmbland]

Once #335 is sorted, this test should pass, so we must remember to remove the xfail mark

[HarmonicReflux]

I think this is related to earlier issue #359

[dalonsoa]

No, it is not. This is something that @tsmbland marked the other day as xfail because of a known cause that will be sorted with #335

[dalonsoa]

@HarmonicReflux , see #381 (comment)