Add a new JSON output format to the vvp/validation-scripts suitable for consumption by other applications (i.e. Dovetail and VNFSDK)

This will be acheived by passing json to the --report-format option at the command line

See https://wiki.onap.org/display/DW/Updated+JSON+Report+Output+for+Validation+Scripts for more details

With this ticket we will also allow the user to customize the output directory using a new option:

--output-directory