temporary fix for FirstRun/LastRun wrong data type

It's a temporary fix for what has been discussed in this elog:
https://cms-logbook.cern.ch/elog/Workflow+processing/17619

In summary, we try to insert data into the database with different data type (int and str) for the same column, and that causes an exception. I still need to find why and where exactly the run numbers are being cast to str.
Maybe give me a couple of days to figure out that...
It's now in  in the RelVal agent and one of the testbed ones.