Create "image_conversion_dir" before creating temporary file

In file "image_utils.py", "create_temporary_file" method is
failing because, CONF.image_conversion_dir folder doesn't exist.

This patch solves the issue by creating image_conversion_dir
directory before calling "create_temporary_file" method.

Change-Id: I546180e0521616fccdaf261d25fd4356d05f0274
Closes-Bug: #1394578
Merge "Create "image_conversion_dir" before creating temporary file"