The IndexBuildCoordinator obtains the Replication Coordinator member configuration using replCoord->findConfigMemberByHostAndPort() in two places. Since the configuration could change before this call returns, it's not clear if this is conceptually a safe thing to do. We should verify that the IndexBuildCoordinator behaves correctly during configuration changes.

(There's currently an actual race, which will be fixed by SERVER-82259, but the issue of stale config data remains)