x/net/http2: TestTransportBody* flaky on android and ppc64

[bcmills]

The x/net/http2.TestTransportBody tests seem to flake with request body larger than specified content length errors at a relatively high rate on certain builders.

Examples:

• android-386-emu:
  • https://build.golang.org/log/d984e27183b94c7e368d94218884779974344556
  • https://build.golang.org/log/1f7126e68b628480fe5a654699de8824eeca44f4
• linux-ppc64-buildlet
  • https://build.golang.org/log/96c9c2893db745808b15290db8d7ad800bd5b773
  • https://build.golang.org/log/dda7e3f43e4ae4a8f29654ff93a82772bd6db199
  • https://build.golang.org/log/638ae27a8305403407f12f1c4e55ee3bd8dc1eab
  • https://build.golang.org/log/7772ce82be9e6ce7a9f2a40974c3a2abcdfa2545

CC @bradfitz @tombergan

[jamie-digital]

I've seen the same behaviour on AWS CodeBuild, which is probably amd64.

[bcmills]

Still failing quite frequently on linux-ppc64-buildlet.

• https://build.golang.org/log/9f52bb48c180c7c62230367b7d91a63695185071
• https://build.golang.org/log/8c385d640b3bb16c08d3eb402484a544d295c03e
• https://build.golang.org/log/a5fcb8e0a08e408e4c31f3725ac1ad664df74a1
• https://build.golang.org/log/543f046ec23ace13b6abe18b31e72e3c9b649da3

Milestoned to 1.14 via #11811.

[ceseo]

cc @laboger

[laboger]

I see this failure intermittently on ppc64le for both power8 and 9 as well as ppc64.

It started soon after this: https://go-review.googlesource.com/c/net/+/181157, which is the change that added the test and the expected error message.

[bcmills]

linux-ppc64-buildlet:

• https://build.golang.org/log/28b1e4180b0c9b983cf7ffb28615d2243c70bfd5

[bcmills]

Also on aix-ppc64, apparently:

• https://build.golang.org/log/473cfbd6a1cffec501b8ebe120bec61088cee5ae

--- FAIL: TestTransportBodyLargerThanSpecifiedContentLength_len3 (0.01s)
    transport_test.go:4519: expected http2: request body larger than specified content length, got <nil>
FAIL
FAIL	golang.org/x/net/http2	14.679s