Update get image file tests

*Updated get_image_file
-Updated tests due to behavior, fixture and config changes
-Removed redundant code
-Updated method calls
*Updated get_image_file_negative
-Updated tests due to behavior, fixture and config changes
-Updated test steps for better clarity
-Updated method call

Change-Id: I64ca5f3bb358335dc1495cb1343f421f8c32c052
Merge "Update get image file tests"