The test had been setting an arbitrary 200ms timeout to allow the
server's handler to set up before timing out. That is not only
potentially flaky on slow machines, but also typically much longer
than necessary. Replace the hard-coded timeout with a much shorter
initial timeout, and use exponential backoff to lengthen it if needed.

This allows the test to be run about 20x faster in the typical case,
which may make it easier to reproduce rare failure modes by running
with a higher -count flag.

For #43120

Change-Id: I1e0d0ec99d5a107fff56e3bcc7174d686ec582d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/361275
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

These tests are empirically flaky on the windows/arm and windows/arm64
builders, with a consistent (but rare) failure mode.

This change skips the test if that particular failure mode is
encountered on those platforms; the skip can be removed if and when
someone has the time to pin down the root cause.

For #43120

Change-Id: Ie3a9a06bf47e3a907c7b07441acc1494a4631135
Reviewed-on: https://go-review.googlesource.com/c/go/+/375635
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

…ndows/arm64

This extends the skip added in CL 375635 to the "_Headers" variant of
the test, since we have observed similar failures in that variant on
the builders.

For #43120

Change-Id: Ib1c97fbb776b576271629272f3194da77913a941
Reviewed-on: https://go-review.googlesource.com/c/go/+/379156
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

These tests are empirically flaky on the windows/arm and windows/arm64
builders, with a consistent (but rare) failure mode.

This change skips the test if that particular failure mode is
encountered on those platforms; the skip can be removed if and when
someone has the time to pin down the root cause.

For golang#43120

Change-Id: Ie3a9a06bf47e3a907c7b07441acc1494a4631135
Reviewed-on: https://go-review.googlesource.com/c/go/+/375635
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

…ndows/arm64

This extends the skip added in CL 375635 to the "_Headers" variant of
the test, since we have observed similar failures in that variant on
the builders.

For golang#43120

Change-Id: Ib1c97fbb776b576271629272f3194da77913a941
Reviewed-on: https://go-review.googlesource.com/c/go/+/379156
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

There is already a skip in case of a later failure in the same test on
these platforms. Skip the failure if it occurs earlier too.

For #43120.

Change-Id: Id530370caa6a7df8cae593f6fdcb66871b86b125
Reviewed-on: https://go-review.googlesource.com/c/go/+/425096
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Damien Neil <dneil@google.com>