Compile for armv8.

"fix init error"

go_binary: remove hardcoded library link path, add pserver client test

* Server recovery from checkpoint

Add go testing into cmake

Add unit test for OpKernel

Add GetEigenDevice To DeviceContext.

FIX: add -lrt for link

fix pybind compile question

OperatorWithKernel

* User can register OpKernel to its Ops. The OpKernelMap saved in
  OperatorWithKernel. Each Op which inherits OperatorWithKernel will
  use `OpKernel::Compute` instead of Run.

Remove Dim::contiguous and Dim::contiguous_strides

add tensor interfaces

Paddle's data block is row-major order, while Dim::contiguous and
Dim::contiguous_strides are based on column-order. So remove them to
prevent misuse.