CCPP-ize get_hydrostatic_energy and remove cam_thermo_formula dependency from check_energy_chng

[jimmielin]

As brought up during the review of #145 (check_energy CCPP-ization), the dependency on cam_thermo_formula in check_energy_chng run and timestep initialize:

I'm not sure how portable the formulas for different dycores are for models beyond CAM, and this doesn't seem to be as easy to work around as the dycore_energy_consistency_adjust_run situation where a different flag could be used. I would suggest perhaps we could leave it as-is so we could CCPP-ize get_hydrostatic_energy and the corresponding formula flags in the future?