Unify `loadGaugeQuda` and `loadSloppyGaugeQuda` as much as possible

[weinbe2]

In lib/interface_quda.cpp, the routines loadGaugeQuda and loadSloppyGaugeQuda, while distinct, do a lot of redundant work. They both contain logic to create the sloppy, preconditioned, and refinement gauge fields.

One easy solution would be to have loadGaugeQuda call loadSloppyGaugeQuda after creating the precise field, which would largely address the problem.

Assigning to myself for simplicity, but I may not get to it for a spell.