Add an option to turn off csv parsing

[oliverlloyd]

This would allow scripts and vars to be passed and prevent parsing errors. (See #72.)

Right now the script only accepts pure file path references in the filepath field of the CSV Config element. It needs this because it uses awk to parse the path and read the file. It reads the file because it distributes the contents line by line into n different files (where n is the number of slaves).

By having a property that disabled this feature we'd allow people to pass in whatever they want here - or whatever JMeter accepts - and it would disable csv distribution. Maybe people don't want their csv data divided up?