CDAP-9148 wrap sparkprogram plugins and change stddev calculation
Change the standard deviation calculation to avoid overflow
concerns. Also wrapping the new sparkprogram plugins so that they
at least get the logging wrapping.
CDAP-9148 refactoring to wrap all pipeline plugins
Refactoring so that any known plugin type instantiated by the
pipeline is wrapped so that the context classloader is set
before any plugin method is called, and so that all certain
methods are timed and a metrics emitted for time spent.
Also performs one part of the fix to stage logging, which is to
set a key in the logging MDC before any plugin method is called.