concurrency_replication_for_backup_restore's WaitForReplication hook should ignore shutdown errors due to quiesce mode

backup_restore.js can call rst.stop() while concurrently running the WaitForReplication hook. After the quiesce mode project, we started failing any new and running isMaster requests with ShutdownInProgress errors.

This means that when we try to create a new replset test fixture here (while a node is being shut down), the hook will fail with a ShutdownInProgress error. This hook should swallow the errors if we're in quiesce mode.