[WFLY-3315] Fix next date computation

CalendarBasedTimeout overrides the 1st day of week value (which is
Locale-dependent) when it computes its firstTimeout in setFirstTimeout().
However it must also override it in the truncate() method to make sure
that comparison between the firstTimeout and its truncated copy is
correct. Bugs will occur if the JVM's Locale has a different value for
the 1st day of the week (e.g. French week starts on monday, while
English week starts on sunday).

JIRA: https://issues.jboss.org/browse/WFLY-3315