Defining the variable "tmp" before try block

In file "image_utils.py", "tmp" variable initialized in try
block. So, if any exception occurred in the try block, then
"tmp" would not be assigned with any value. Because of this
finally block will raise an exception like "local variable
tmp tried to use before the assignment".

This patch resolves that issue by defining "tmp" variable before
try block.

Change-Id: I9d8c8eaaeba0a7aab7ebfc791b9ddd967f324184
Closes-Bug: #1394548
Merge "Defining the variable "tmp" before try block"