Stop PoolReadConfig and PoolWriteConfig creating different instances of EvtPersistencySvc
While debugging LAr Super Cell creation in old and new style configuration. @bwynne and I noticed that the CA-based configuration has two instances of EvtPersistencySvc one with the default name and one called EventPersistencySvc, while the old-style configuration only has one instance called EventPersistencySvc. The default-named instance is created in PoolWriteConfig.py. This MR just adds the name, so that the versions created by the PoolReadCfg and PoolWriteCfg methods can be merged.