Fix docker tmp/ and extensions/ handling for docker.

[simcop2387]

This should address #4485 and #4474

We try to do the rename first since it'll be faster and more reliable for setups where it works, but when it doesn't we fall back to using shutil.move() so that it can handle when there's multiple filesystems involved (usually docker, or symlinks involved).

[simcop2387]

Tested and working for me

[AUTOMATIC1111]

the idea is to prevent a situation where a script is only copied halfway and the program stops working and you end up with incomplete copy of the repo. The solution I'd prefer is to make a temp dir inside extensions dir then.

[yolofy]

Make it happen