Polish CronTriggerTests and assess daylight savings time issue

This test polishes CronTriggerTests and modifies the
daylightSavingMissingHour() test to help analyze why the test fails
for CET if the minute value for the last completion time falls between
0 and 9 minutes.

Associated broken build:

https://ge.spring.io/s/epphj7vruwcn6/tests/:spring-context:test/org.springframework.scheduling.support.CronTriggerTests/testDaylightSavingMissingHour(LocalDateTime,%20TimeZone)%5B2%5D?expanded-stacktrace=WyIwIl0