private TransitRegionStateProcedure createAssignProcedure(RegionStateNode regionNode,
    ServerName targetServer) {
    regionNode.lock();
    try {
      return regionNode.setProcedure(TransitRegionStateProcedure.assign(getProcedureEnvironment(),
        regionNode.getRegionInfo(), targetServer));
    } finally {
      regionNode.unlock();
    }
  }
Create an assign TransitRegionStateProcedure. Does NO checking of RegionState. Presumes
appriopriate state ripe for assign.
@see #createAssignProcedure(RegionInfo, ServerName, boolean, boolean)
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/AssignmentManager.java