Refactored test_images.py and images.py

Refactored test_images.py to include separate tests for each
Method in the Context Class

Also removed default values of arguments to image context class in
images.py which are now mandatory

Change-Id: Iaa510ea10b6f54eb0968382e8ea648fe4dcc288d
Merge "Refactored test_images.py and images.py"