Changed the way we name downloaded zip files in `build_usd.py` to avoid file name collisions.

[Cewein]

Description of Change(s)

Changed the way we name downloaded zip files in build_usd.py to minimise the chance of file collision. Files from a GitHub or GitLab repository previously only had their version numbers as their names. Now, they will incorporate the project name and the version.

I assume other URLs provide this (i.e., Boost and HDF5).

Fixes Issue(s)

• https://github.com/PixarAnimationStudios/OpenUSD/issues/457

• [ ] I have verified that all unit tests pass with the proposed changes
• [X] I have submitted a signed Contributor License Agreement

[jesschimein]

Filed as internal issue #USD-9603

:heavy_exclamation_mark: Please make sure that a signed CLA has been submitted!

[jesschimein]

/AzurePipelines run

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