Add a Runner class to SippyCup
user
```ruby
require 'yaml'

module SippyCup
  class Runner
    def initialize(path)
      @options = YAML.load_file File.expand_path(path)
    end

    def prepare_command
      ['scenario', 'source', 'destination', 'max_concurrent', 'calls_per_second', 'number_of_calls'].each do |arg|
        raise "Must provide #{arg}!" unless @options[arg]
      end
      command = "sudo sipp"
      source_port = @options['source_port'] || '8836'
      sip_user = @options['sip_user'] || '1'
      command << " -i #{@options['source']} -p #{source_port} -sf #{File.expand_path @options['scenario']}"
      command << " -l #{@options['max_concurrent']} -m #{@options['number_of_calls']} -r #{@options['calls_per_second']}"
      command << " -s #{sip_user}"
      if @options['stats_file']
        stats_interval = @options['stats_interval'] || 10
        command << " -trace_stats -stf #{@options['stats_file']} -fd #{stats_interval}"
      end
      command << " > /dev/null 2> &1" unless @options['full_sipp_output']
      command
    end

    def run
      command = prepare_command
      p "Preparing to run SIPp command: #{command}"
      result = system command
      raise "SIPp failed! Try running the scenario with the full_sipp_output enabled for more information" unless result
      p "Test completed successfully!"
      p "Statistics logged at #{File.expand_path @options['stats_file']}" if @options['stats_file']
    end

  end
end```
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