LANG-983 DurationFormatUtils does not describe format string fully

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/lang/trunk@1573786 13f79535-47bb-0310-9956-ffa450edef68
Add some more tests

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/lang/trunk@1573787 13f79535-47bb-0310-9956-ffa450edef68