YARN-913 rename field and javadoc describing valid entry pattern to make clear its purpose
YARN-913 sync field names in .toString() with renamed values in record
YARN-913 RegistryOperationUtils logic for getting current username (including env var override) tested
YARN-913 name stored in RegistryPathStatus is short name. It gets reinserted in some of the utility code, and rebuilt in some other places
YARN-913 registry path status update
YARN-913 move contents of record operations to RegistryOperationsUtils (too many static classes), replace all uses of RegistryOperations.listFully() with the new RegistryOperationsHelper.statChildren(), and make purge more robust against parallel deletions in the process