MGM: change space from XrdOucString to std::string + minor changes to avoid double lookups in Quota.cc
Since we don't use XrdOucString specific details in any of the call sites use std::string as this avoids conversions in multiple places and helps towards unifying the various scheduler calls
Signed-off-by: Abhishek Lekshmanan abhishek.lekshmanan@cern.ch