Modify ocean core barotropic subcycle to reuse halo data structure

[Larofeticus]

Modify the subcycle halo exchanges of sshSubcycle and normalBarotropicVelocitySubcycle to follow the alternative framework routines which reuse the halo exchange group data structure.

Speed tested on 256 Cori KNL nodes with 8448 mpi ranks, 4 threads per rank, mid resolution mesh, and ~170 cells per rank, the performance gain is 25%.

There is also a cleanup of the tracking of remaining valid halo cells and edges as the subcycle progresses; this removes the extra exchange edge case, and allows correct behavior for config_num_halos != 3 (although using a halo size other than 3 diminishes performance).

[Larofeticus]

@mark-petersen @philipwjones