Merge TestOnlyLocalExternalIPs, TestOnlyLocalLoadBalancing, and
TestOnlyLocalNodePorts together into TestExternalTrafficPolicyLocal.
Drop the assertIPTablesRulesEqual tests in favor of
runPacketFlowTests.
Remove TestOnlyLocalNodePortsNoClusterCIDR; the relevant bits of the
"no local detector" case are already fully covered by
TestInternalExternalMasquerade.