Fully initialize atmosphere_{heat,momentum}_diffusivity in several schemes

[DomHeinzeller]

This issue is a follow up for issue #639 .

PR #641, which addressed #639, changed the vertical dimension of some arrays from vertical_dimension_minus_one to vertical_dimension. The CCPP schemes that use these variables as intent(out) however do not initialize the arrays for the additional vertical level.

We need to revisit all CCPP schemes that use these arrays (simply look at the files changed in #641) and add the missing initialization for the extra vertical level.