Add clearAll() and deprecate clear() in favor or clearMap(). Use the active voice in Javadocs. clearAll must be used from tests to avoid creating test failures due to test ordering.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1593347 13f79535-47bb-0310-9956-ffa450edef68