[Thread] move infra network utilities to IntegrationTestUtils.kt

This CL moves setUpInfraNetwork(), tearDownInfraNetwork() and
startInfraDeviceAndWaitForOnLinkAddr() into IntegrationTestUtils.kt
because they'll also be used by Internet Access test cases which will be
in a new file.

The methods are refactored in Kotlin to be easier used in new test
cases. The new test cases will also be written in Kotlin.

Bug: 356770473

Change-Id: I2e5788ba87f9f86dd14d382db0b0de791bcbce6a
2 files changed