Fall back to nerdvegas Windows Docker Image

[j0yu]

Fixes Windows CI tests failing on forked repositories where ${gh_user}, e.g. wwfxuk, does not have a DockerHub image available.

For example, from #749 for commit cee7216

• nerdvegas runs https://github.com/nerdvegas/rez/runs/379212610
• wwfxuk's run https://github.com/wwfxuk/rez/runs/379212678

Here is this branch's Windows CI on:

• nerdvegas runs https://github.com/nerdvegas/rez/runs/379578231
• wwfxuk runs https://github.com/wwfxuk/rez/runs/379552284

[nerdvegas]

Cheers for the fix!

I do wonder if the image fallback is needless complication though. Would anyone else really want to be hosting their own rez Windows CI docker image (and if they did, they could just change their own workflow anyway)?

For the sake of simplicity, should we not just replace ${gh_user} with nerdvegas?

[j0yu]

Would anyone else really want to be hosting their own rez Windows CI docker image (and if they did, they could just change their own workflow anyway)?

I guess so, it would probably make sense if they're PRing the Windows Dockerfiles and want to be able to create images themselves.

There's also mention of moving to use GitHub Docker Packages for these images too in #789 which might be better to keep things within the GitHub ecosystem.

For the sake of simplicity, should we not just replace ${gh_user} with nerdvegas?

Done! Also simplified to just the run command as it will should automatically pull from DockerHub

[bfloch]

This was just useful during development of the image, but it can be easily controlled in forks etc.

Thanks for the fix!