Pass ops and args fields to wtperf via command line

Currently arguments and operations fields are passed into the performance testing framework via a json arg_file containing:

[{

  "arguments": ["-C log=(enabled,file_max=1M),session_max=256", "-o threads=((count=128,updates=1))"], 

  "operations": ["update"] 

}] 

but this creates a lot of unnecessary files and is not the intended use of arg_files, which are meant to contain multiple configurations for a single test run.

Instead we can pass these fields in via the command line.

Definition of Done:
operations and arguments fields can be passed in via the command line rather than via an external .json file