Rename all private functions to have underbars preceeding the function name

All private functions should use the generally [accepted practice](https://stackoverflow.com/questions/2289293/is-there-a-convention-for-naming-private-functions-in-bash) of preceding the function name with underbars.  As an example in [test-utils.sh](https://github.com/FlossWare/scripts/blob/master/bash/test-utils.sh#L196), the function name should be renamed ```__unit-test()```.