[Core] fail to download s3 py modules

[laysfire]

Why are these changes needed?

In our scenario, the users would upload working dir or py modules to s3 and submit job with filling security credential in runtime env.
Currently Ray doesn't support fetch security credential information from user runtime env, so the job would fail when download s3 resources.
This PR is to fix this issue.

Related issue number

None

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(