Add test for Vpn#prepare() to check if the SecurityException will be thrown when the caller is not the SYSTEM_UID and doesn't have CONTROL_VPN permission and its package doesn't match the oldPackage or the newPackage. Ignore-AOSP-First: It's a part of security patches. Bug: 191276656 Test: atest FrameworksNetTests:VpnTest Change-Id: Ibe0b245561b00442a6377fb849603f8b9026e9c4 Merged-In: Ibe0b245561b00442a6377fb849603f8b9026e9c4