Improve/check robustness of the IOUtils.hpp random matrix generators

[brian-kelley]

PRs #661 and #678 helped a lot, but we should still go though all the functions and make sure they handle all reasonable inputs correctly. For example, the fix I did to kk_sparseMatrix_generate didn't make it into kk_generate_diagonally_dominant_sparse_matrix, so it's possible other functions still have issues.

Example (noticed by @ndellingwood): In a later PR probably should add a check that ncols > 0 in case someone calls the routine with ncols == 0 (lines 197-200).