Test webservice timeout

Trying to fix this issue:

```
PASS: test-reauthorize 18 /pamreauth/password-no-prepare
PASS: test-reauthorize 19 /pamreauth/password-bad-secret
PASS: test-transport 21 /transport/echo-large/child
**
cockpit-ws:ERROR:src/ws/test-webservice.c:361:expect_control_message: assertion failed (expected_command == message_command): ("open" == "ping")
PASS: test-cgroupmonitor 1 /cgroup-monitor/new
FAIL: test-webservice 1 /web-service/close-error
PASS: test-cgroupmonitor 2 /cgroup-monitor/get-samples
PASS: test-cgroupmonitor 3 /cgroup-monitor/new-sample
```

https://travis-ci.org/cockpit-project/cockpit/jobs/25492678