crypto/x509: TestSystemVerify failures on windows-*-2008 builders

[josharian]

Seen on a trybot run for CL 38164:

--- FAIL: TestSystemVerify (45.44s)
verify_test.go:429: #7: unexpected error: x509: certificate signed by unknown authority
verify_test.go:438: #7: wanted 1 chains, got 0
FAIL
FAIL crypto/x509 46.342s

https://storage.googleapis.com/go-build-log/1d573555/windows-amd64-gce_8ca3ccb2.log

For that run, it failed on both amd64 and 386.

[bradfitz]

Weird. Unless a system cert expired?

[josharian]

But a subsequent run passed, with the same CL rebased up a single commit.

Maybe gce system clock flakiness?

[bradfitz]

These are fresh VMs, single-use per build. Dunno.

[mknyszek]

Recent instance on windows-386 trybot?

##### Testing without libgcc.
--- FAIL: TestSystemVerify (0.95s)
    verify_test.go:565: #8: unexpected error: x509: certificate signed by unknown authority
    verify_test.go:574: #8: wanted 1 chains, got 0
FAIL
FAIL	crypto/x509	2.624s
2019/05/15 22:50:06 Failed: exit status 1
2019/05/15 22:50:07 FAILED

https://storage.googleapis.com/go-build-log/c197b9dc/windows-386-2008_583fee2b.log