Keystore 2.0: Make Legacy VPN settings ready for Keystore 2.0

Keystore 2.0 no longer stores vpn profiles. It still offers a
Legacy VPN profile store, to access existing profiles.

Test: N/A
Bug: 171305607
Bug: 171305388
Change-Id: I40dea0b9c3824b56814ae4c2fb6c7663c7d97af5