BayesQuasi Produces Different Outputs on macOS

[cailafinn]

Describe the bug
The values produced for the Prob and Result outputs from BayesQuasi do not match the reference files within a reasonable tolerance (written as 1e-10 in the system test).

To Reproduce

1. Remove the skip from the BayesQuasiTest systemtest in the Mantid repository.
2. Run the test on macOS.
3. Load the mismatch files and reference files and observe the differences (the "superplot" function is useful for this).

Expected behavior
The output should be the same (or at least reasonably similar) on all platforms.
The skipTests method can be removed from BayesQuasiTest and the test still passes on all platforms.

Screenshots

Platform/Version (please complete the following information):

• OS: macOS