Add sites to input dataset when trustSiteList is enabled

This adds the site whitelist locations to the input dataset locations when a WorkQueueElement is created at the GWQ level, when xrootd is enabled (trustSiteList=True). Otherwise WorkQueueElement is not pulled to wmagent. I realized of this working with data stored at cmseos.fnal.gov (T3_US_FNALLPC), even if I enable xrootd and set T1_US_FNAL in the site whitelist, the agent never pull work.