Small difference between hydra and usd sphere primitives

[sebastienblor]

In order to tessellate sphere primitives in the usd reader, like Hydra does, we used the code from https://github.com/PixarAnimationStudios/OpenUSD/blob/release/pxr/usdImaging/usdImaging/implicitSurfaceMeshUtils.cpp#L41

However, we are still getting tiny discrepancies between both versions, which is failing several tests.

[autodesk-oss-arnold-bot[bot]]

Issue synced internally to ARNOLD-14045