Fix WifiDialogActivityTest broken

- The ShadowWifiManager class is not working as expected

- Use Mockito class instead of Shadow class

Bug: 175369329
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=WifiDialogActivityTest

Change-Id: Idbc851c4d9702be23561c2c48c9d7d077e5f452e
2 files changed