migraged dotted names of mmapv1 options from "storage" to "storage.mmapv1"
storage.mmapv1.directoryPerDB
storage.mmapv1.journal.commitIntervalMs
storage.mmapv1.journal.debugFlags
storage.mmapv1.nsSize
storage.mmapv1.preallocDataFiles
storage.mmapv1.quota.enforced
storage.mmapv1.quota.maxFilesPerDB
storage.mmapv1.smallFiles
storage.mmapv1.syncPeriodSecs
dotted names (without the ".mmapv1" component) of mmapv1 options before migration
will still be accepted but a warning will be raised at startup.