Avoid creating empty modulefile directories when using modaltsoftname

[geimer]

Use module name from naming scheme rather than deriving path from install directory. Fixes #2167 for my use cases.

@boegel I'm not sure about the module symlinking at https://github.com/hpcugent/easybuild-framework/blob/master/easybuild/framework/easyblock.py#L1527, but my gut feeling is that it was broken as well and will be implicitly fixed, too.

[boegel]

lgtm, but we've learned the hard way not to fix bugs without making sure we have a test that triggers it (to avoid reintroducing the same problem later)

done in geimer#16

[geimer]

@boegel I had to fix the unit test you provided in geimer#16 as it was assuming Lua module syntax (hard-coded). Please have quick look at the fix and let me know whether it's OK or whether you have any suggestions for improvement.

[boegel]

@geimer Oops, I indeed overlooked that even though I made a mental note to fix that before passing it to you, sorry. Fix looks great, thanks!

[boegel]

Going in, thanks for the bugfix @geimer!