net: TestLookupGoogleSRV and TestLookupGmailMX flaky on builders

[quasilyte]

During CL98775: build742ae1bd

--- FAIL: TestLookupGoogleSRV (5.01s)
	lookup_test.go:76: lookup _xmpp-server._tcp.google.com on 10.3.240.10:53: read udp 10.0.7.69:46483->10.3.240.10:53: read: connection refused
--- FAIL: TestLookupGmailMX (10.01s)
	lookup_test.go:113: lookup gmail.com on 10.3.240.10:53: read udp 10.0.7.69:41650->10.3.240.10:53: read: connection refused
FAIL
FAIL	net	29.755s

The failure disappeared during second try-bots run.

Most likely a temporary network issue on builder.
Filling this in case this pops up again in near time.

[andybons]

I’m guessing you’re unable to repro this locally?

/cc @bradfitz for the builders and net

[quasilyte]

Tried src/race.bash locally. It passes.
I didn't passed those though:

["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" "HOSTNAME=buildlet-linux-kubestd-rn88973d0" "IN_KUBERNETES=1" "META_BUILDLET_BINARY_URL=http://storage.googleapis.com/go-builder-data/buildlet.linux-amd64" "META_BUILDLET_HOST_TYPE=host-linux-kubestd" "KUBERNETES_SERVICE_HOST=10.3.240.1" "KUBERNETES_SERVICE_PORT=443" "KUBERNETES_SERVICE_PORT_HTTPS=443" "KUBERNETES_PORT=tcp://10.3.240.1:443" "KUBERNETES_PORT_443_TCP=tcp://10.3.240.1:443" "KUBERNETES_PORT_443_TCP_PROTO=tcp" "KUBERNETES_PORT_443_TCP_PORT=443" "KUBERNETES_PORT_443_TCP_ADDR=10.3.240.1" "DEBIAN_FRONTEND=noninteractive" "HOME=/root" "WORKDIR=/tmp/workdir" "GOROOT_BOOTSTRAP=/go1.4" "GO_BUILDER_NAME=linux-amd64-race" "GOBIN="]

...because I don't know what KUBERNETES_ variables affect and whenever they are significant in this situation.

[mdempsky]

Flaked on linux-amd64 too: https://storage.googleapis.com/go-build-log/e903c73f/linux-amd64_470f8c78.log

[bcmills]

darwin-arm64-corellium:

• https://build.golang.org/log/13d3386f108efca836c4b1a460de34a11d8c6d30
• https://build.golang.org/log/2968da334e70e9e6a6cdf9888d0263b098f31edf

[bcmills]

CC @dmitshur @toothrot