Move requests-logging setting to global scope

This should happen at import, since the __init__ may have been run in a different proc, and the cache pickled, since then.

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/38522554

Reviewed at https://rbcommons.com/s/twitter/r/1022/
Sync of https://github.com/pantsbuild/pants/commit/7d44ea3e59df4f5ce3fdc8d9d19595a3a2bbe607