Prevent HNS integration failures during network cleanup

[Copilot]

The Windows integration job failed in TestNetworkFlags with HCN_E_ADAPTER_NOT_FOUND when a new test network was created before HNS completed asynchronous teardown of the previous one.

• Test cleanup
  • Poll for deleted networks to disappear from HNS before allowing subsequent test setup.
  • Preserve the existing fixed-name test network workflow while preventing adapter teardown races.

fori:=0; i<20; i++ {
time.Sleep(500*time.Millisecond)
if_, err:=GetNetworkByName(networkName); err!=nil {
return
}
}