time: TestTicker failures on netbsd-amd64-8_0 builder

[bcmills]

--- FAIL: TestTicker (1.26s)
    tick_test.go:70: saw 5 errors
    tick_test.go:32: 10 20ms ticks took 250.987124ms, expected [160ms,240ms]
    tick_test.go:32: 10 20ms ticks took 251.555254ms, expected [160ms,240ms]
    tick_test.go:32: 10 20ms ticks took 251.282407ms, expected [160ms,240ms]
    tick_test.go:32: 10 20ms ticks took 251.501105ms, expected [160ms,240ms]
    tick_test.go:32: 10 20ms ticks took 251.463514ms, expected [160ms,240ms]
FAIL
FAIL	time	4.698s

We may just need to widen the accepted intervals a bit on this builder.

See also #35692.

CC @ianlancetaylor

2020-02-15T16:40:12-6917529/netbsd-amd64-8_0
2020-02-05T22:19:16-e5b9c10/netbsd-amd64-8_0

[katiehockman]

Saw the same flake in openbsd-amd64-68 today

--- FAIL: TestTicker (1.81s)
    tick_test.go:79: saw 5 errors
    tick_test.go:37: 10 20ms ticks took 361.739892ms, expected [240ms,360ms]
    tick_test.go:37: 10 20ms ticks took 362.25355ms, expected [240ms,360ms]
    tick_test.go:37: 10 20ms ticks took 362.221384ms, expected [240ms,360ms]
    tick_test.go:37: 10 20ms ticks took 362.225653ms, expected [240ms,360ms]
    tick_test.go:37: 10 20ms ticks took 362.289081ms, expected [240ms,360ms]
FAIL
FAIL	time	5.030s
FAIL

Full log: openbsd-amd64-68_399b8d79.log.txt

[ianlancetaylor]

2021-04-20T15:45:02-9dd71ba/openbsd-amd64-68
2021-03-30T21:20:51-e0ce0af/linux-ppc64le-buildlet
2020-12-21T17:56:36-53c984d/openbsd-amd64-68
2020-11-13T15:00:23-35455ff/netbsd-386-9_0
2020-10-28T21:52:53-615c7c1/netbsd-386-9_0

[gopherbot]

Change https://golang.org/cl/313849 mentions this issue: time: increase slop for TestTicker

[ianlancetaylor]

The test is inherently flaky. CL 313849 will increase the slop, which in itself will fix all but one of the recent failures. I also added a sleep at each attempt to try to get past an overloaded system.