Revert "Revert "Revert "Revert "Add path interposer""""

This reverts commit 09f4540d.

Fixes the raw call to net.Listen in the tests to go through the listen()
helper and use the long socket path fallbacks.

Removes the use of timeouts from the tests -- the behaviors being tested
did not rely on timeouts, so removing them will reduce the flakiness if
the build is heavily loading the machine at the same time the test is
running.

Also fixes some potential nil pointer dereferences.

Test: OUT_DIR=<really long> m blueprint_tools
Test: `while .../soong-ui-build-paths/test/test; do sleep 0.01; done` with a build running
Change-Id: I16d44be7517bc415f1c808284088f4ba40df3bfa