To use the library in the submodule instead of the pypi one set variable:
PYTHONPATH='./fortiosapi'
in python console
os.environ['PYTHONPATH'] = './fortiosapi'
To correctly get the referenced submodules please use the --recursive option of git clone like this:
git clone https://github.com/fortinet-solutions-cse/fortiosapi-examples.git --recursive
pull
git pull --recurse-submodule