nebraska: Implement payload search

Target and source directories can now be searched for payloads matching
an update or install request. Update and install requests are matched
based on request type, appid, and delta payload information. Matches for
a given request are logged, but no response is generated.

BUG=chromium:892450
TEST=Manual, unittesting

Change-Id: I80af2b5463f8e59608c917179020a6b7b15eb85c
Reviewed-on: https://chromium-review.googlesource.com/1282308
Commit-Ready: Colin Howes <chowes@google.com>
Tested-by: Colin Howes <chowes@google.com>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
2 files changed