PRF: cache RunS*, EventDescriptor on insert
PRF: cache RunS*, EventDescriptor on insert

Save a lookup or two

arkilic/metadatastore,NSLS-II/metadatastore,tacaswell/metadataStore,tacaswell/metadataStore,ericdill/databroker,ericdill/databroker,NSLS-II/metadatastore,hhslepicka/metadatastore,arkilic/metadatastore,hhslepicka/metadatastore