promoting as a member of DQMStore and remove static

```
//Need to make sure only one thread creates the ofstream
{
   std::unique_ptr<std::ofstream> tempStream{ new ofstream("histogramBookingBT.log") };
   std::ofstream* expected=nullptr;
   if( stream_.compare_exchange_strong(expected,tempStream.get()) ) {
      //this thread won the race so we are using its tempStream
      tempStream.release();
   }
}
```