TZUpdater support for "vanguard" format (JDK 7u only)

TZUpdater does not operate as expected for JDK 7u(javazic data source). To allow it to perform the same operation as JSR 310(JDK 8 and above), a temporary workaround was put in place which involves translating vanguard to rearguard before computation of javazic data sources.

This is similar to what the IANA script does here: https://github.com/eggert/tz/blob/master/ziguard.awk, by plain parsing vanguard and translating to rearguard.

The workaround is fragile and can break. TZUpdater code needs to be updated to be resilient with tzdata changes.