fix(lock): release the lock files that were actually taken

[loicsapone]

initLockFile() only flagged the deployment as holding a lock after every server
had been visited:

$context->exec(function (Session $session) { ... $session->touch($lockFile); });
$this->hasLock = true;   // never reached if a later server throws

With several servers, if a later one is already locked, the exception leaves the
earlier servers with a lock file that clearLockFile() then refuses to remove. Those
servers stay locked forever: every subsequent deployment fails with "A deployment is
already in progress" until someone passes --force or deletes the file by hand.

Locks are now recorded server by server, as soon as they are taken, and released the
same way — a server locked by another deployment is left untouched.

Tests

New LockListenerTest, 3 cases. The one covering the orphan lock fails on main.