skypilot_wrapper hardcodes gcpuser when copying files back

[krzentner]

Ideally we would be able to use skypilot with any skypilot backend, but the current skypilot wrapper assumes the absolute path on the remote host will be in /home/gcpuser. I'm not sure the cleanest way to solve this, since it's not clear what directory the command will run in. Perhaps we can inject some code into the skypilot yaml to standardize the absolute output path?