Changes in Locale Data from JDK 9 onwards

Working on MAGNOLIA-8369 I discovered some tests started to fail because of differences in date time formatting compared to JDK 8. (E.g. the short format in the French locale changed from 27/09/13 to 27/09/2013).

The reason is JDK 9 switching to CLDR as the default locale data source.  The previous behaviour can be restored through the java.locale.providerssystem property if desired.

Our documentation should point out these changes, how they might affect customers and how customers can restore the previous behaviour if they need to.