ImportError: libcublas.so.9.0: cannot open shared object file

You will need to update your LD_LIBRARY_PATH, so that it points to the /usr/local/cuda-9.0/lib64.
Add the following line to your .bashrc file (or any other terminal you use)

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/cuda-9.0/lib64/