This is an attempt to fix the flaky test of TestSwarmNodeTaskListFilter in 25029. Basically this fix adds a check to wait until 3 containers has already up, before processing `node tasks ...`. This might fix 25029. Signed-off-by: Yong Tang <yong.tang.github@outlook.com> Upstream-commit: 63c0366bc9a7f326ad61cdfa69fa860cf844a2c7 Component: engine