Added config subsetting and joining

Refactored two functions, and cleaned up long lines in test.

BUG=chromium:234294
TEST=run_all_test.py

Change-Id: I01c0b482d5b422e136a192ba8ad8f28d531b94e1
Reviewed-on: https://chromium-review.googlesource.com/177559
Reviewed-by: Byron Kubert <byronk@chromium.org>
Commit-Queue: Byron Kubert <byronk@chromium.org>
Tested-by: Byron Kubert <byronk@chromium.org>
3 files changed