mxnet: added 1.3.0 (#9236)
mxnet: added 1.3.0 (#9236)

* add version 1.3.0
* change build parameters, install process
  * mxnet will not compile against spack's nnvm and dmlc so we must use
    the distributions provided by the source package.
* also removed 'bin' installation as mxnet is just a shared library.
* improve BLAS linking
* remove unnecessary args
* added variant for python bindings

LLNL/spack,iulian787/spack,LLNL/spack,LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack,LLNL/spack,iulian787/spack,iulian787/spack