Update VPN tests to mock out createAttributionContext

This allows VpnManagerServiceTest continues to work after
adding an attribution tag to VpnManagerService

Bug: 278943609
Test: atest FrameworksNetTests:android.net.connectivity.com.android.server.VpnManagerServiceTest
Change-Id: I4228a7fb308b8d01aee53f0734f4c5753908473a
Merged-In: I4228a7fb308b8d01aee53f0734f4c5753908473a
1 file changed