public boolean waitMetaLoaded(Procedure<?> proc) {
    return metaLoadEvent.suspendIfNotReady(proc);
  }
Wait until AM finishes the meta loading, i.e, the region states rebuilding.
@see #isMetaLoaded()
@see #waitMetaAssigned(Procedure, RegionInfo)
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/AssignmentManager.java