NIFI-4151: Updated UpdateAttribute to only create JAXB Context once; …

[markap14]

…Minor performance tweaks to standard validators and StatusMerge.prettyPrint; updated AbstractConfiguredComponent to not create a new ValidationContext each time that validate is called but only when needed; updated FlowController, StandardControllerServiceProvider, and StandardProcessGroup so that component lookups can be performed using a ConcurrentMap at FlowController level instead of having to perform a depth-first search through all ProcessGroups when calling findProcessor(), findProcessGroup(), findXYZ()

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[mcgilman]

Will review...

[mcgilman]

@markap14 Looks like the proposed changes are causing unit test failures.

[mcgilman]

Thanks @markap14! The update has addressed the test failures and this has been merged to master.