lowmemorykiller: Run the showmem notifier when killing

When the lowmemory killer starts killing adj 0 tasks, it's useful to
be able to see the state of other memory in the system. Call the
showmem notifier to get other clients to dump out their state.

Change-Id: Ie3b1d47149f0108b42b7961fd47a8cc5efe2c590
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>