Look on pytorch servers when installing pip deps (#3477)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3477

When installing the executorch pip package for CI jobs, look on the
pytorch servers when resolving dependencies. This lets the executorch
package depend on pytorch pre-release and nightly versions.

Also run the llava setup with `-x` to make it easier to debug failures.

imported-using-ghimport

Test Plan: Imported from OSS

Reviewed By: mikekgfb

Differential Revision: D56857486

Pulled By: dbort

fbshipit-source-id: dc2bc1c7e8ee59ad9461f2b5eb8e7da785485ad7