start: Prevent grep its own process

Although confined by the process id, there is still a great probability
(~10%) `grep` can sieze its owner process because the predictable
process count of a newly started OS, like:
```
2014-08-12 11:12:59: [root@localhost ~]# ps 241 |grep 'sleep 1000'
2014-08-12 11:12:59:   241 pts/0    S+     0:00 grep --color=auto sleep 1000
```

This patch uses a trick to solve this problem.

Signed-off-by: Hao Liu <hliu@redhat.com>