Improved string representation of array values in jmx connector

Arrays were being rendered using the default toString representation.
So, an Array would be rendered as something like [Ljava.lang.String;@4da91ced.
Arrays are now rendered as a string representation of the contents of the array.
The string representation consists of a list of the array's elements,
enclosed in square brackets ("[]").  Adjacent elements are separated by ", ".

Fixes #1632