collect os info for mac

This CL adds logic to collect os infor for both engine and framework mac builders before and after test execution.
A test build: https://luci-milo.appspot.com/raw/build/logs.chromium.org/flutter/led/keyonghan_google.com/a604c77f8177a2bd8e08430da41640e03756e7c70d9475f757ea5b14a0f8699d/+/annotations

Bug: https://github.com/flutter/flutter/issues/67934
Change-Id: I55aa32ad06f3920a4e81ac5ce061ee78cb1a14f8
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/7260
Reviewed-by: Godofredo Contreras <godofredoc@google.com>
Reviewed-by: Nurhan Turgut <nurhan@google.com>
Commit-Queue: Keyong Han <keyonghan@google.com>