atomic.py: use a different name for images cache
atomic.py: use a different name for images cache

Detected by pylint. The 'images' method was being hidden by the 'images'
attribute. This can cause confusion and thus it is better to rename them
so that they differ.

lsm5/atomic,cdrage/atomic,sallyom/atomic,lsm5/atomic,charliedrage/atomic,sallyom/atomic,charliedrage/atomic,rh-atomic-bot/atomic,rh-atomic-bot/atomic,cdrage/atomic,dustymabe/atomic,dustymabe/atomic