Move logic of generate_system_health_csv to .py file

Move logic of generate_system_health_csv to generate_system_health_csv.py in order to allow for imports.
Move into tools/perf/core

Bug: chromium:723636
Change-Id: Ied8df78b51200110f8baa61b0e7cba8a617e2b72
Reviewed-on: https://chromium-review.googlesource.com/675667
Commit-Queue: Lori Oliver <loloangela@google.com>
Reviewed-by: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#504153}
3 files changed