Install numpy from source for Python 3.5 to fix the nightly build.

Change: 147395987

tensorflow/tools/ci_build/install/install_python3.5_pip_packages.sh

@@ -70,7 +70,11 @@ pip3.5 install --upgrade protobuf==3.0.0
 rm -rf /usr/lib/python3/dist-packages/six*
 
 # Install numpy, scipy and scikit-learn required by the builds
-pip3.5 install --upgrade numpy
+
+# numpy needs to be installed from source to fix segfaults. See:
+# https://github.com/tensorflow/tensorflow/issues/6968
+# This workaround isn't needed for Ubuntu 16.04 or later.
+pip3.5 install --no-binary=:all: --upgrade numpy
 
 set +e
 SCIPY_VERSION="0.17.1"