Indeed CMake, a list is not a directory...

After testing a Python module, the build was broken because the test
created a __pycache__ dir, which CMake tried to install as a file because:

a) `if(IS_DIRECTORY foo)` requires a full path to work

b) For CMake, `IS_DIRECTORY(foo)` is not the same as `IS_DIRECTORY foo`

c) CMake is a pain sometimes
Make testmodule.py more Pythonic
Ignore Python files
Remove \t tab to avoid failure in testmodule.py
We can now test mount with testmodule.py: remove the test main()