VpnSettings: show connected VPN even if deleted

So there's a way to disconnect from it, if someone deletes all the
keystore entries and the VPN doesn't actually exist any more (but
is still sitting around in memory somewhere keeping the connection
alive).

Bug: 29093779
Fix: 32880676
Test: runtest -x tests/app/src/com/android/settings/vpn2/VpnTests.java
Change-Id: I97671a74af746e5baaa5be0b5cff24e2b1766f53