cmd/go: test timeouts without useful debugging output on darwin builders

[bcmills]

There are numerous occasional test timeouts on the darwin-amd64-race builder in the logs.

I note that the windows-amd64-race builder sets GO_TEST_TIMEOUT_SCALE=2:
https://github.com/golang/build/blob/916311cec4e1738aae572fe49767cebdc0351144/dashboard/builders.go#L2067

I suspect that we may need to do the same for the darwin-amd64-race builder to reduce flakiness.

CC @andybons

2020-04-27T23:05:16-42c4899/darwin-amd64-race
2020-04-17T04:26:54-29d925d/darwin-amd64-race
2020-04-16T15:31:20-4eaf855/darwin-amd64-race
2020-04-10T18:45:24-37470c0/darwin-amd64-race
2019-10-11T16:34:01-ba108c9/darwin-amd64-race
2019-10-04T21:22:55-5f4aa5d/darwin-amd64-race
2019-09-24T04:19:31-e29d276/darwin-amd64-race
2019-09-16T22:14:49-115e4c9/darwin-amd64-race
2019-09-06T21:22:26-8a8cf5b/darwin-amd64-race
2019-06-29T13:17:15-623d653/darwin-amd64-race
2019-06-28T20:10:05-2e0cd2a/darwin-amd64-race
2019-06-28T20:09:48-91c385b/darwin-amd64-race
2019-06-28T20:00:59-3b040b7/darwin-amd64-race
2019-06-27T20:43:26-f205ae3/darwin-amd64-race
2019-06-26T20:17:35-9acd2d6/darwin-amd64-race
2019-06-26T18:38:59-06f709a/darwin-amd64-race
2019-06-26T16:35:14-60f14fd/darwin-amd64-race
2019-06-26T03:59:57-adf8883/darwin-amd64-race
2019-06-25T21:30:39-343b7fa/darwin-amd64-race
2019-06-25T17:51:25-a6ad626/darwin-amd64-race
2019-06-25T16:43:17-3f83c83/darwin-amd64-race
2019-06-24T21:26:46-5f7e9ce/darwin-amd64-race
2019-06-14T16:46:12-80f8913/darwin-amd64-race
2019-06-13T17:12:09-f83c44e/darwin-amd64-race
2019-06-13T14:14:02-55d31e1/darwin-amd64-race
2019-06-13T03:58:11-418c7d8/darwin-amd64-race
2019-06-12T22:17:38-c0c6cee/darwin-amd64-race
2019-06-12T18:03:46-f44404e/darwin-amd64-race
2019-06-11T17:54:27-9f76566/darwin-amd64-race
2019-06-10T23:23:39-ef84fa0/darwin-amd64-race
2019-06-10T20:32:36-5ce1819/darwin-amd64-race
2019-06-10T16:19:39-8f296f5/darwin-amd64-race
2019-06-05T17:53:53-e9a136d/darwin-amd64-race
2019-06-05T17:25:56-195e753/darwin-amd64-race
2019-06-05T00:53:14-ac921da/darwin-amd64-race
2019-05-24T21:34:53-385b2e0/darwin-amd64-race
2019-05-17T22:32:30-1ab063c/darwin-amd64-race
2019-05-13T17:01:25-db2bf15/darwin-amd64-race
2019-05-09T21:13:46-56c1cf3/darwin-amd64-race
2019-05-09T21:13:23-60f6763/darwin-amd64-race
2019-05-09T21:13:19-fe67ce2/darwin-amd64-race
2019-05-09T15:32:36-b6f59cb/darwin-amd64-race
2019-04-30T18:29:07-888bac1/darwin-amd64-race
2019-04-29T22:35:35-98c5a56/darwin-amd64-race
2019-04-29T04:05:29-d016330/darwin-amd64-race

[bcmills]

This seems to be one of the larger sources of dashboard flakes at the moment (CC @golang/osp-team).

2020-08-24T19:20:59-bb99874/darwin-amd64-race
2020-08-22T12:35:47-8acbe4c/darwin-amd64-race
2020-08-20T15:21:34-822dca4/darwin-amd64-race
2020-08-16T14:23:50-d303630/darwin-amd64-race
2020-06-03T22:07:42-429d2c5/darwin-amd64-race
2020-05-09T23:17:17-c9442dc/darwin-amd64-race
2020-05-07T23:22:45-78aa4af/darwin-amd64-race
2020-05-02T20:20:16-2d323f9/darwin-amd64-race
2020-05-01T15:02:30-e3b0e3d/darwin-amd64-race

[bcmills]

Looks like it's not just the darwin-amd64-race builder. We might need to rework the timeout logic in the cmd/go tests to get more useful information.

2021-02-19T00:04:56-bb6efb9/darwin-amd64-race
2021-02-18T18:12:04-f3c2208/darwin-amd64-race
2021-01-20T09:06:08-928bda4/darwin-amd64-race
2021-01-07T17:51:29-e60cffa/darwin-amd64-race
2021-01-07T17:49:47-6da2d3b/darwin-amd64-race
2020-12-22T18:36:29-c06a354/darwin-amd64-10_15
2020-12-02T20:17:57-2d0258d/darwin-amd64-race
2020-12-01T21:41:39-7430266/darwin-amd64-race
2020-11-19T19:35:35-add4593/darwin-amd64-10_15
2020-11-12T13:47:13-9ef65ff/darwin-amd64-race
2020-11-07T16:59:55-5e371e0/darwin-amd64-race
2020-10-22T23:00:42-f1aa0b0/darwin-amd64-race
2020-10-19T15:00:02-2a206c7/darwin-amd64-race
2020-10-15T18:26:33-497ea06/darwin-amd64-race
2020-10-13T17:36:36-ad53103/darwin-amd64-race
2020-10-08T08:53:13-542693e/darwin-amd64-race
2020-09-29T16:12:04-39a426d/darwin-amd64-race
2020-09-27T02:23:55-7bb6fed/darwin-amd64-race
2020-09-19T05:13:19-ccf581f/netbsd-386-9_0
2020-09-15T18:48:09-3ab825d/darwin-amd64-race
2020-08-28T16:40:41-ae7b6a3/darwin-amd64-10_15
2020-08-27T21:13:46-2963443/darwin-amd64-race
2020-08-25T14:47:39-02f4452/darwin-amd64-race
2020-08-24T19:20:59-bb99874/darwin-amd64-race
2020-08-22T12:35:47-8acbe4c/darwin-amd64-race
2020-08-20T15:21:34-822dca4/darwin-amd64-race
2020-08-16T14:23:50-d303630/darwin-amd64-race
2020-06-03T22:07:42-429d2c5/darwin-amd64-race