Changes to build to fix creation of wheels. (#840)

* Pass DPYTHON_EXECUTABLE into cmake for arrow and for ray.

* Add cython to setup.py install_requires.

* Revert custom code for finding python in cmake.

* Correctly find arrow on CentOS.

* In cmake, don't find PythonLibs, just find PYTHON_INCLUDE_DIRS.

* Fix typo.

* Do not use boost shared libraries when building arrow.

* Add six to the setup.py install_requires because it is needed by pyarrow.

* Don't link numbuf against boost_system and boost_filesystem.

* Compile boost when we are on Linux.

* Make numbuf find the correct boost libraries.

* Only use find_package Boost on Linux, suppress output when building boost.

* Changes to wheel building scripts, install cython in mac script.

* Compile flatbuffers ourselves on Linux and pass it in when compiling Arrow.

* Clean up build_flatbuffers.sh and build_boost.sh scripts a little.

* Install cython when building linux wheel.

python/setup.py

@@ -81,12 +81,15 @@ setup(name="ray",
       # The BinaryDistribution argument triggers build_ext.
       distclass=BinaryDistribution,
       install_requires=["numpy",
+                        "cython",
                         "funcsigs",
                         "click",
                         "colorama",
                         "psutil",
                         "redis",
                         "cloudpickle >= 0.2.2",
+                        # The six module is required by pyarrow.
+                        "six >= 1.0.0",
                         "flatbuffers"],
       entry_points={"console_scripts": ["ray=ray.scripts.scripts:main"]},
       include_package_data=True,