lrdp_V2 : Fix for broken ion_buffer_parse.py

ion_buffer_parse.py is looping continuously in case
of task list corruption or task's thread corruption.
using the task list iterator API which is handling
all such task list corruption cases.

cleanup code in memusages.py and use the task list
iterator API.

Change-Id: I611cba31d8df14e29fc3250233d9ad1e99e919ee
Signed-off-by: Ankur Bansal <ankban@codeaurora.org>