Multiple file support

[adrijshikhar]

fix #2215

Add multiple file support with --iteration-data flag. Right now it checks whether the location is array or not. If its an array then check whether it has an object inside it or not. If it has no object, then it is an array of location and data is parsed for each location and then passed on, and if not an array, location variable is treated as string.

[adrijshikhar]

the issue i am facing is that when the test is performed, in forEach , async.waterfall is asynchronous and forEach is synchronous. So when the test is performed, callback is called, before forEach getting executed and empty array is passed. I have two possible solutions for this.

1. To convert async.waterfall to await or promises
2. make it recursive callback function and finally return the appended values.

I prefer the recursive way. I could really use some help.
@shamasis @codenirvana