--hosts option for Newman distributed mode.

- Includes related validations.
DistributedRunner module

- Takes care of all the processing for distributed runs
- Takes in the list of hosts parsed from the --hosts option and other
command line options
- Once all the responses are received (regardless of if they are
successful or not), the results are consolidated and exported as JSON
to the --outputFile
Use the DistributedRunner module in main

- Execute using the DistributedRunner when --hosts is supplied.