8079773: java/util/logging/LogManager/TestLoggerNames.java
Summary: Fixed a race condition in the test which was responsible of the intermittent failure.
Reviewed-by: mchung

7113878: LogManager - namedLoggers should be ConcurrentHashMap instead of Hashtable
Summary: namedLoggers is now a ConcurrentHashMap. findLogger is updated to take benefit of the change.
Reviewed-by: dholmes, lancea, martin, mchung, plevart
Contributed-by: Peter Levart <peter.levart@gmail.com>, Daniel Fuchs <daniel.fuchs@oracle.com>