Interesting failure on WindowsRS5: https://jenkins.dockerproject.org/job/Docker-PRs-WoW-RS5-Process/3063/console

11:59:47 --- FAIL: TestHealthKillContainer (8.12s)
11:59:47     health_test.go:57: assertion failed: error is not nil: Error response from daemon: Invalid signal: SIGUSR1

That test was added recently in #39454, but rewritten in a commit in the same PR: f8aef6a

In that rewrite, there were some changes:

• originally it was skipped on Windows, but the rewritten test doesn't have that skip:

  testRequires(c, DaemonIsLinux) // busybox doesn't work on Windows

• the original test used SIGINT, but the new one uses SIGUSR1