Add CUDNN 3 and 4 to the CUDA 7.0 images.

[elezar]

I have added Docker files for CUDNN 3 and 4 to the CUDA 7.0 images.

From the release notes, it seems as if CUDA 7.0 is the minimum requirements, and I run on a server where I am able to use Docker, but the drivers are not up to date for use with CUDA 7.5. I do, however, need CUDNN 3 (at least) for use with Caffe.

As a side note, there does seem to be quite a bit of duplication in the Docker files. Is there generation automated in some way?

[flx42]

Thank you for the PR!
To accept your contribution, we need you to sign our CLA, see here:
https://github.com/nvidia/nvidia-docker#issues-and-contributing

887838d looks good, but I'm in the process of modifying how we fetch cudnn v4. You will probably need to amend your commit after I'm done. cudnn v3 will not change.
026a2f7 looks fine.
a48765c I disagree, you don't need to put tabs everywhere in a Makefile. Only before commands.

Regarding your question of duplication in Dockerfiles: no we don't have automated generation. Maybe we will in the future, but right now there are still a few differences between versions.

[flx42]

I added 7.0 cudnn4 myself, since I was asked to do a Caffe image. I will still take your first 2 patches for 7.0 cudnn3 + the custom docker executable. I will rebase your code myself, just send us the CLA!

[elezar]

Great! With regards to the tabs in a48765c, I know that tabs are only required for the commands. The spacing where the cudnn versions were specified, was just inconsistent (mixed tabs and spaces). I can use spaces instead if that would be better.

I have just emailed the CLA and CCed you, @flx42.

[flx42]

Merged, thanks!