YANR-913 registry client has factory; chooses auth mech: anon, sasl or digest based on conf parameters
YARN-913 add initial user guide and design patterns
YARN-913 add ability to debug JAAS tests
YARN-913 slight cleanup of RegistrySecurity
YARN-913 improvements to debug why UGI.login is failing
YARN-913 testSecureLogins ... more debugging
HADOOP-11117 UGI HadoopLoginModule doesn't catch & wrap all kerberos-related exceptions
YARN-913 log  registry, service & UGI @ debug
YARN-913 lots of debugging and extra tests understanding why a regression since last week was preventing Hadoop UGI logins
YARN-913 some improvements and javadocs to CuratorService and RMRegistryOperationsService