When running using led, DEPOT_TOOLS_REPORT_BUILD might not be set, and
bots will try to collect metrics.

Set DEPOT_TOOLS_COLLECT_METRICS so metrics are not collected on this
case.

Recipe-Nontrivial-Roll: build
Recipe-Nontrivial-Roll: infra
Recipe-Nontrivial-Roll: build_limited_scripts_slave
Recipe-Nontrivial-Roll: chromiumos
Change-Id: I8b1083b31ef6daf87d24544a990bee863543aa1d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2946935Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>