* fix(test): address flaky S3 distributed lock integration test
Two root causes:
1. Lock ring convergence race: After waitForFilerCount(2) confirms the
master sees both filers, there's a window where filer0's lock ring
still only contains itself (master's LockRingUpdate broadcast is
delayed by the 1s stabilization timer). During this window filer0
considers itself primary for ALL keys, so both filers can
independently grant the same lock.
Fix: Add waitForLockRingConverged() that acquires the same lock
through both filers and verifies mutual exclusion before proceeding.
2. Hash function mismatch: ownerForObjectLock used util.HashStringToLong
(MD5 + modulo) to predict lock owners, but the production DLM uses
CRC32 consistent hashing via HashRing. This meant the test could
pick keys that route to the same filer, not exercising the
cross-filer coordination it intended to test.
Fix: Use lock_manager.NewHashRing + GetPrimary() to match production
routing exactly.
* fix(test): verify lock denial reason in convergence check
Ensure the convergence check only returns true when the second lock
attempt is denied specifically because the lock is already owned,
avoiding false positives from transient errors.
* fix(test): check one key per primary filer in convergence wait
A single arbitrary key can false-pass: if its real primary is the filer
with the stale ring, mutual exclusion holds trivially because that filer
IS the correct primary. Generate one test key per distinct primary using
the same consistent-hash ring as production, so a stale ring on any
filer is caught deterministically.
