Errors in pip installation part go unnoticed by rez install.py

[instinct-vfx]

This is with rez-2.47.9 on windows 10 (but this should be cross platform)

The rez install.py script uses subprocess.Popen to call python -m pip install . but ignores returncodes etc. See line 39 ff : https://github.com/nerdvegas/rez/blob/2.47.9/install.py#L39

def run_command(args, cwd=source_path):
    if opts.verbose:
        print("running in %s: %s" % (cwd, " ".join(args)))
    p = subprocess.Popen(args, cwd=source_path)
    p.wait()

If the installation fails this goes unnoticed and still considered a success. A case that i ran into was caused by PYTHONPATH injecting older versions of libraries that caused an error.

I think all i would like to add is checking the return code and raising an exception if the call failed.

Any objections?

[instinct-vfx]

Added PR for testing. I only replaced the Popen + p.wait() call with a single check_output() call. In my (windows) testing this worked fine for working installation and raises an exception and aborts installation if the pip call fails.