Start using n1-highcpu-8 machine type instead of n1-highcpu-4
for the freebsd-amd64-race builder.

The freebsd-amd64-race builder has produced good test results
for the x/tools repo for a long time, but by now it has started
to consistently fail for reasons that seem connected to it having
only 3.6 GB memory. The Windows race builders needed to be bumped
from 7.2 GB to 14.4 GB to run successfully, so this change makes
a small incremental step to bring freebsd-amd64-race closer in
line with other builders. If memory-related problems continue to
occur with 7.2 GB, the next step will be to go up to 14.4 GB.

The freebsd-amd64-race builder is using an older version of FreeBSD.
We may want to start using a newer one for running tests with -race,
but that should be a separate change so we can see the results of
this change without another confounding variable.

Also update all FreeBSD builders to use https in buildletURLTmpl,
because it's expected to work fine and will be more consistent.

Updates golang/go#36444
Updates golang/go#34621
Updates golang/go#29252
Updates golang/go#33986

Change-Id: Idfcefd1c91bddc9f70ab23e02fcdca54fda9d1ac
Reviewed-on: https://go-review.googlesource.com/c/build/+/214433
Run-TryBot: Carlos Amedee <carlos@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

This is a followup to CL 214433. Start using n1-highcpu-16 machine type
instead of n1-highcpu-8 for the freebsd-amd64-race builder.

Increasing the RAM from 3.6 GB to 7.2 GB has helped golang/go#36444
significantly: the builder stopped failing consistently on x/tools
and resulted in many data races being uncovered in golang/go#36605.

However, by now, it has started to fail consistently again. This
time it seems to be due to low performance, causing the tests in
golang.org/x/tools/internal/lsp/regtest package to fail due with
"context deadline exceeded" errors.

FreeBSD is one of the ports that stays visible when "show only first-
class ports" is checked on build.golang.org. The other -race builders
have all been upgraded to the n1-highcpu-16 machine type by now out
of necessity.

It seems fair to provide the FreeBSD port with an equal amount of
resources, even if the increased memory isn't strictly required yet.
Once this change is applied, if the failures persist, we can be more
confident that the problem is due to the code or the port, rather
than due to this -race builder having 2𝗑 less CPU and RAM resources
compared to other -race builders.

An alternative is to increase timeout for this builder type, but I'm
opting to defer exploring that after equalizing the machine type.

For golang/go#36444.
For golang/go#34621.
For golang/go#29252.
For golang/go#33986.

Change-Id: I41f149365128c7bc6f576c778ac07618acc04612
Reviewed-on: https://go-review.googlesource.com/c/build/+/227859
Reviewed-by: Alexander Rakoczy <alex@golang.org>