This commit expands IKEv2 VPN CTS testing to ensure that given a
successful IKEv2 negotiation, the VPN network will be correctly set up.
Additionally, it verifies that the stopProvisionedVpnProfile will
teardown the VPN network.
Bug: 148582947
Test: atest CtsNetTestCases:Ikev2VpnTest
Change-Id: Ib6635f0068200ac0172515989fbdee5c3d49e231