Revert "Revert "Refs #8807 Add some system tests for ConvFit.""

This reverts commit a2137e58d2ccbdce33d9a24859a8e30f9fe698d0.
Refs #8800 Relax tolerance.
Refs #8803 Update tolerance levels.
Refs #8800 Update with more accurate parameters for IRIS.
Merge branch 'feature/8803_convfit_sys_tests' into develop