Make testVpnNetworkActive more deterministic. am: abc306b5e9

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/13425313

Change-Id: I5b7901958bf96b0cee80c6124e004e57da0992cd
tree: f0d704650dd58aa898a918add67b894a4ab885e8
  1. core/
  2. services/
  3. tests/