Support Process pool feature

Support Process pool feature

Launchpad is introducing a process pool. The process pool class creates
child processes, which are used to execute application launch requests or
to create loader processes. This feature is used to improve performance.
The PSS memory usage of candidate processes is not high, typically ranging
from 400 to 500.

Change-Id: I0142e7c15d12295741c46fa5e203caa664dea0d9
Signed-off-by: Hwankyu Jhun <h.jhun@samsung.com>