all: add basic trace to gddo

This uses Stackdriver trace API to trace search, package requests
as well as background tasks. It also traces outbound requests to
VCS's and remote_api calls.

Change-Id: Ice82c1fbd267eefa4bad9d6674dc39ef10a1c874
Reviewed-on: https://go-review.googlesource.com/68472
Reviewed-by: Ross Light <light@google.com>
6 files changed