cmd/pprof: vendored internal/driver has flaky tests

[mvdan]

This issue was already reported upstream weeks ago: google/pprof#328

I am filing this since it's happened a few times that we know of, so this one should help us track the fix better and help others who stumble upon the same failure.

For search purposes, the test in question is TestHttpInsecure.

Assigning to self, to update the vendored packages once the upstream bug is fixed.

[mvdan]

Another potential question is why we need to run the vendored library tests, or why we vendor their test files at all. But I assume we do want that for one reason or another, such as being extra sure that all platforms are supported.

[gopherbot]

Change https://golang.org/cl/105275 mentions this issue: cmd/vendor/.../pprof: update to 0f7d9ba1