migrate from phEDExNodetocmsName to PNNtoPSN

@ticoann @ericvaandering 

fix for issue #5341. Note that the new API PNNtoPSN returns a list of possible PSNs where as the phedexNodetocmsName returned a single PSN string. I have therefore just taken the first element in this list. Does this sound reasonable?

please review

--Alex
Hi Alex, We still need PSN, since that is what Glidein matches job to site. (Unless it changed now)
In general to submit the job we need a PSN and other cases (i.e. recording location to PhEDEx, etc) PNN is used.