Documentation and manual regression tests need updating after #1217 merge

[bjonkman]

#1217 changed the r-test suite, but there are a few things it missed:

• [x] The manualRegressionTest.py script should be changed so that it works with the updated execute*RegressionCase.py files. It doesn't currently run because it is calling scripts with incorrect arguments. (Note: I am working on updating that in a different PR because merging dev into my current work disabled my ability to test.)
• [ ] The documentation needs to update the changes to the regression tests. Here are some places that I noticed are out of date:
  • [ ] https://openfast.readthedocs.io/en/dev/source/testing/regression_test.html
  • [ ] https://openfast.readthedocs.io/en/dev/source/testing/regression_test.html#executing-with-python-driver
  • [ ] https://openfast.readthedocs.io/en/dev/source/testing/regression_test_windows.html#windows-with-visual-studio-regression-test
  • [ ] The r-test readme: https://github.com/OpenFAST/r-test#readme
• [ ] It would be helpful to have the default RTOL and ATOL values listed in #1217 to also be listed in the documentation (and in the scripts?) or possibly actually make them defaults in the python scripts.
• [x] I think the Bokeh version needs to be at least 2.4 for these updates, too. I'm getting this error with Bokeh 1.4: Error generating plots: gridplot() got an unexpected keyword argument 'width' Bokeh v2.4.3 wants the 'plot_width' keyword to be replaced with 'width', but that keyword doesn't exist in earlier versions.