Create vdiff_holtslag_boville_diff_free_atm SDF and add to suite_cam7

CAM7 using CLUBB uses the HB PBL scheme in levels above CLUBB using the modified `compute_hb_free_atm_diff` (CCPP'ized variant `hb_diff_free_atm_exchange_coefficients_run`).

A snapshot should be taken of the `vertical_diffusion_section` using a CAM7 configuration and used to test this part of code similarly to how the CAM4 version of full HB is being tested now.

When testing is shown to be bit-for-bit, the contents of that file (which are reduced compared to CAM4) should be added to the `suite_cam7` SDF file for testing with the CAM-SIMA `FCAM7` compset.