mm: reap tasks only killed by low memory killer

Reap tasks that are killed by ulmk only.

Change-Id: I4af044b3b8fb5fe1dcef6bac70c475cf949d0505
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
[isaacm@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>