Merge pull request #7761 from jhseu/ubuntu

Use Ubuntu 14.04 for the 1.0 branch GPU build.

tensorflow/tools/ci_build/Dockerfile.gpu

-FROM nvidia/cuda:8.0-cudnn5-devel
+FROM nvidia/cuda:8.0-cudnn5-devel-ubuntu14.04
 
 MAINTAINER Jan Prach <jendap@google.com>
 
+# In the Ubuntu 14.04 images, cudnn is placed in system paths. Move them to
+# /usr/local/cuda
+RUN cp /usr/include/cudnn.h /usr/local/cuda/include
+RUN cp /usr/lib/x86_64-linux-gnu/libcudnn* /usr/local/cuda/lib64
+
 # Copy and run the install scripts.
 COPY install/*.sh /install/
 RUN /install/install_bootstrap_deb_packages.sh