[automerger skipped] Add a test for starting the legacy VPN. am: c9e026f4e9 -s ours

am skip reason: Change-Id I3c4a94181bd71df68121fa0f71669fa4fa588bdd with SHA-1 4d64450516 is in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/12330622

Change-Id: Ieff977b6742a93b3a8f335ff6022cf1fbdcec2e7