optional cuda helper path by environ var

pytorch/cuda/setup.py

 from setuptools import setup
 from torch.utils.cpp_extension import BuildExtension, CUDAExtension
+import os
+
+CUDA_HELPER = os.environ.get('CUDA_HELPER', '/usr/local/cuda/samples/common/inc')
 
 setup(
     name='moe_cuda',
@@ -10,8 +13,8 @@ setup(
                 'moe.cpp',
                 'moe_cuda_kernel.cu',
                 ],
-            extra_compile_args={'cxx': ['-I/usr/local/cuda/samples/common/inc'],
-                                'nvcc': ['-I/usr/local/cuda/samples/common/inc']}
+            extra_compile_args={'cxx': ['-I{}'.format(CUDA_HELPER)],
+                                'nvcc': ['-I{}'.format(CUDA_HELPER)]}
         )
     ],
     cmdclass={