Fix Block policy accounting of lumis

When a run white/blacklist is present, the accounting of lumis is screwed up
and it only reports a number of lumis equal to the number of runs accepted in a block.

Fix it by properly retrieving the number of lumis per run from DBS, it doesn't
require extra queries as the information is already available but it wasn't being
returned by the listRuns call of teh DBS[2-3]Reader class.