Experiment on vgg flower, 2 trainers, 1ps.
    more trainer could have more speedup.

    After:
    Pass = 0, Iters = 327, Speed = (7.52) img/s
    Before:
    Pass = 0, Iters = 385, Speed = (6.77) img/s

* test_patch_mkldnn

* use patch file

* follow comments

* fix patch

disable building tests and examples when install mkldnn
skip -Werror=unused-result

* "re-commit "

* "picked up"

* "fix ci"

* "fix pdb hang up issue in cuda 9"

* "fix cuda9 error"

* "change commit id"

* "remote git tag"