This is necessary for EthernetNetworkFactory because it uses
the static lib NetworkFactory which needs to test where it runs.
Wifi services also need this for its own factories.
Bug: 183902758
Test: ClientModeImplTest
OemWifiNetworkFactoryTest
TelephonyNetworkFactoryTest
UntrustedWifiNetworkFactoryTest
WifiNetworkFactoryTest
Change-Id: I73cc38d7857934fe50995c666915662de4c154ce