Include timezone on NiFI log messages

While we can stress the importance of using NTP to make sure clocks across multiple system running NIFi remain in sync, we cannot enforce a requirement that all system set their systems to a common timezone. The logs currently do not show the timezone on each log entry which can make it confusing for users when trying to trace log events across multiple NiFI instances that are configured for different timezones. This would be increasing difficult if logs were moved to a central logging server.