Update gpu docker file

[mhamilton723]

The Gpu Docker does not build on master (#540) for several reasons

1. Tensorflow defaults to cudadnn_6.0
2. The issue raised and solved in
   bazel GPU build error with fatal error: external/nccl_archive/src/nccl.h: No such file or directory #327 (comment)

This PR solves these two issues and the resulting docker image builds and passes all

[tensorflow-jenkins]

Can one of the admins verify this patch?

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[mhamilton723]

I signed it!

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We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for the commit author(s). If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
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[googlebot]

CLAs look good, thanks!

[mhamilton723]

What are the thoughts of the tf serving team? @chrisolston Is there a specific process for requesting code review?

[kirilg]

Thanks for the contribution Mark!