In the recent 20e9f3369 we made HealthChangeRequest machine requests
include a NodeKey, as it was the oddball machine request that didn't
include one. Unfortunately, that code was sometimes being called (at
least in some of our integration tests) without a node key due to its
registration with health.RegisterWatcher(direct.ReportHealthChange).
Fortunately tests in corp caught this before we cut a release. It's
possible this only affects this particular integration test's
environment, but still worth fixing.
Updates tailscale/corp#1297
Change-Id: I84046779955105763dc1be5121c69fec3c138672
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>