Remove main package dependency on boost-python and boost-numpy (#1569483)
    
    Rename all subpackages using python2 from boost-xxx to boost-xxx2.
    Split new subpackage boost-python2-devel out of boost-devel.
    Split new subpackage boost-openmpi-python2-devel out of boost-openmpi-devel.
    Split new subpackage boost-mpich-python2-devel out of boost-mpich-devel.
    Enable conditional build for python2 packages.