Problems running integration test outside of a supported stack

rhl reports that when running the integration test on his personal machine, it fails because the fluxmodeldata package is not available. That's a very large data package, so it's not part of the usual distribution. If it's not available, we should stop at the point it's required.

Also, he noticed the following (apparently non-fatal) "fatal" error:

+ git -c lfs.batch=true clone --branch= --single-branch https://github.com/Subaru-PFS/drp_stella_data
Cloning into 'drp_stella_data'...
warning: Could not find remote branch  to clone.
fatal: Remote branch  not found in upstream origin