Fixed the can not kill some process using libprocessgroup

In DoKillProcessGroupOnce function, if process has a child process, pids set
will be clear probability and initialPid will not be killed, when the pid
is equal to initialPid.

Test: manual - start duomi app and remove it use recent apps key
Change-Id: Ifb9f4acacd725d2c367e547d2b5512807bb44fec