This commit fixes two flaky test scenarios:
1. testRemoveLockedAddr: Add synchronization to wait for the dial to
start before asserting that the address is locked. Previously, the
test could race and check the lock state before session negotiation
began.
2. testTowerSwitch: Use wait.Predicate for RemoveTower since the
address may still be locked by an active session, causing
intermittent failures.
Gijs van Dam
09379d0381