Instagram test and Instagram node fixes

This is my work on adding the Instagram tests. A few issues might need to be sorted. I'll make comments in-line detailing these.
I'm not convinced using the indirection of the```IMAGE``` variable in place of the constant ```"image"``` adds much to the readability of this code? It also seems somewhat inconsistent with your direct use of ```"photo"```, ```like```, ```"link"```, ```"file"```, etc.