bad DBS API usage

[belforte]

in
https://github.com/CMSCompOps/TransferTeam/blob/master/consistency_check/SCC/SCCUtils.py
the DBS client API is re-created at every iteration inside the main loop.
THis is very inefficient, slow and uselessly heavy on DBS.
SHould be initialized outside the loop and then used once for each filename.