Libzip missing from dense-flow

[asafarevich]

This is same issue as yjxiong/temporal-segment-networks#237
However, I am not sure how I would be able to get the docker build AND use the denseflow lib provided.
Shortened error below

-- Found CUDA: /usr/local/cuda-8.0 (found suitable exact version "8.0") 
-- Could NOT find LIBZIP (missing:  LIBZIP_LIBRARY) 
-- Boost version: 1.58.0
-- Found the following Boost libraries:
--   python
CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
LIBZIP_LIBRARY
    linked by target "denseflow" in directory /home/ubuntu/anet2016-cuhk/lib/dense_flow
    linked by target "extract_cpu" in directory /home/ubuntu/anet2016-cuhk/lib/dense_flow
    linked by target "extract_warp_gpu" in directory /home/ubuntu/anet2016-cuhk/lib/dense_flow
    linked by target "extract_gpu" in directory /home/ubuntu/anet2016-cuhk/lib/dense_flow

-- Configuring incomplete, errors occurred!
See also "/home/ubuntu/anet2016-cuhk/lib/dense_flow/build/CMakeFiles/CMakeOutput.log".
See also "/home/ubuntu/anet2016-cuhk/lib/dense_flow/build/CMakeFiles/CMakeError.log".
make: *** No targets specified and no makefile found.  Stop.
Failed to build Dense Flow. Please check the logs above.

The last part of Dense Flow failing was added from https://github.com/yjxiong/temporal-segment-networks/blob/012104d0e3104d25689ae9c4fdccffd4e818a1bb/build_all.sh#L56

[asafarevich]

I also tried using @yjxiong solution from yjxiong/temporal-segment-networks#62 to install libzip, but its already installed

Reading package lists... Done
Building dependency tree       
Reading state information... Done
libzip-dev is already the newest version (1.0.1-0ubuntu1).