[v6r10] SiteDirector optimizations and fixes

NEW: SiteDirector - do not touch sites for which there is no work available
NEW: SiteDirector - allow sites not in mask to take jobs with JobType Test
NEW: SiteDirector - allow 1 hour grace period for pilots in Unknown state before aborting them
CHANGE: Use non-plural form of the job requirement options ( PilotType, GridCE, BannedSite, SubmitPool ), keep backward compatibility with a plural form
FIX: CREAMComputingElement - extra checks for validity of returned pilot references