Extract IPsec and test network utility methods

This patch moves some test setup functions to util classes in
preparation for IKEv2 VPN tests which will use those same utilities.

Bug: 148582947
Test: atest IpSecManagerTunnelTest; passing
Change-Id: I9aeafa45ab515ce72a72c3de6f70fb26e32e7fd4
Merged-In: I9aeafa45ab515ce72a72c3de6f70fb26e32e7fd4
(cherry picked from commit 30432fa7640603c1e746b7d8c83e2e6052d8f967)
3 files changed