uid_sys_stats: log task io with a debug flag

Add a hashmap inside each uid_entry to keep track of task name and io.
Task full name is a combination of thread and process name.

Bug: 63739275
Change-Id: I30083b757eaef8c61e55a213a883ce8d0c9cf2b1
Signed-off-by: Yang Jin <yajin@google.com>