Docker builds on non-Linux hosts

[tjtelan]

Our current docker driver shiplift has a long-standing bug with performing the equivalent of docker exec on MacOS hosts.

I assume that this will also be a problem on Windows, but I don't have an environment to verify.

[tjtelan]

Currently I'm using the git version of shiplift (as opposed to the released crate) and testing with MacOS 11.1 (Big Sur).

Confirmed that containerized builds work as expected! Hoping that the crate releases a new version with the fix included.

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I'm currently downloading a Win10 Enterprise VM with the intention of installing orbital to test this out. Depending on how that goes, I might close this issue and re-open a Windows-specific issue.