cmd/bench: add flag overrides for all environment variables

This change adds a flag for the experiment and baseline GOROOTs, as well
as a flag for the branch. This both adds documentation as to where
cmd/bench gets these values from, and allows users running this command
manually to override them without modifying their environment.

Change-Id: Iba9e3bc70687989fe6fc40e3a810b21aa5091dfe
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/385735
Reviewed-by: Michael Pratt <mpratt@google.com>
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
1 file changed