Failing to start test server?

https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8928496548465681632/+/steps/net_unittests_on_Ubuntu-16.04/0/logs/SSLClientSocketReadTest.Read__x2f_1/0

[E2018-11-29T12:01:33.392060-08:00 20962 0 annotate.go:241] original error: remove /b/swarming/w/ir/.swarming_module_cache/vpython/7a191e/lib/python2.7/site-packages: directory not empty
[E2018-11-29T12:01:33.392107-08:00 20962 0 annotate.go:241]
[E2018-11-29T12:01:33.392121-08:00 20962 0 annotate.go:241] goroutine 1:
[E2018-11-29T12:01:33.392135-08:00 20962 0 annotate.go:241] #0 go.chromium.org/luci/vpython/venv/venv.go:475 - venv.(*Env).createLocked()
[E2018-11-29T12:01:33.392152-08:00 20962 0 annotate.go:241]   reason: failed to remove existing root
[E2018-11-29T12:01:33.392169-08:00 20962 0 annotate.go:241]
[E2018-11-29T12:01:33.392181-08:00 20962 0 annotate.go:241] #1 go.chromium.org/luci/vpython/venv/venv.go:272 - venv.(*Env).ensure.func1()
[E2018-11-29T12:01:33.392194-08:00 20962 0 annotate.go:241]   reason: failed to create new VirtualEnv
[E2018-11-29T12:01:33.392206-08:00 20962 0 annotate.go:241]
[E2018-11-29T12:01:33.392218-08:00 20962 0 annotate.go:241] #2 go.chromium.org/luci/vpython/venv/venv.go:957 - venv.mustReleaseLock()
[E2018-11-29T12:01:33.392231-08:00 20962 0 annotate.go:241] #3 go.chromium.org/luci/vpython/venv/venv.go:258 - venv.(*Env).ensure()
[E2018-11-29T12:01:33.392243-08:00 20962 0 annotate.go:241] #4 go.chromium.org/luci/vpython/venv/venv.go:328 - venv.(*Env).withImpl()
[E2018-11-29T12:01:33.392255-08:00 20962 0 annotate.go:241] #5 go.chromium.org/luci/vpython/venv/venv.go:168 - venv.With()
[E2018-11-29T12:01:33.392270-08:00 20962 0 annotate.go:241] #6 go.chromium.org/luci/vpython/run.go:62 - vpython.Run()
[E2018-11-29T12:01:33.392282-08:00 20962 0 annotate.go:241] #7 go.chromium.org/luci/vpython/application/application.go:318 - application.(*application).mainImpl()
[E2018-11-29T12:01:33.392303-08:00 20962 0 annotate.go:241] #8 go.chromium.org/luci/vpython/application/application.go:402 - application.(*Config).Main.func1()
[E2018-11-29T12:01:33.392320-08:00 20962 0 annotate.go:241] #9 go.chromium.org/luci/vpython/application/support.go:46 - application.run()
[E2018-11-29T12:01:33.392332-08:00 20962 0 annotate.go:241] #10 go.chromium.org/luci/vpython/application/application.go:401 - application.(*Config).Main()
[E2018-11-29T12:01:33.392356-08:00 20962 0 annotate.go:241] #11 vpython/main.go:93 - main.mainImpl()
[E2018-11-29T12:01:33.392368-08:00 20962 0 annotate.go:241] #12 vpython/main.go:99 - main.main()
[E2018-11-29T12:01:33.392381-08:00 20962 0 annotate.go:241] #13 runtime/proc.go:201 - runtime.main()
[E2018-11-29T12:01:33.392393-08:00 20962 0 annotate.go:241] #14 runtime/asm_amd64.s:1333 - runtime.goexit()
[20076:20076:1129/120133.393482:19845256672:ERROR:local_test_server_posix.cc(167)] Could not read server_data_len
[20076:20076:1129/120133.393776:19845256955:ERROR:ssl_client_socket_unittest.cc(830)] Could not start SpawnedTestServer
../../net/socket/ssl_client_socket_unittest.cc:1444: Failure
Value of: StartTestServer(SpawnedTestServer::SSLOptions())
  Actual: false
Expected: true
Stack trace:
#0 0x55d72e5b775c testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop()
#1 0x55d72e5b7139 testing::internal::AssertHelper::operator=()
#2 0x55d72d9d0174 net::SSLClientSocketReadTest_Read_Test::