Reorganize file to have public API before private helpers (#990)

Summary:
Pull Request resolved: #990

# This stack:
* Adding tests for download_logs/
# This diff:
* In both the download_logs.py and test file, reorganize the functions so that the public API comes before private helper methods

Reviewed By: marksliva

Differential Revision:
D36861913

LaMa Project: L1089718

fbshipit-source-id: 5704169674dae1ed32658633015bbbfdb6082499

Author: Logan Gore