Repair working init script on ubuntu :)

'/bin/sh' is old and bad stuff. If we use '/bin/sh', and it is not alias to /bin/bash we will have various problem with 'test': 

:~# /etc/init.d/serf restart
/etc/init.d/serf: 65: /etc/init.d/serf: [[: not found
Stopped Serf Agent

If we use 'bash', we don't have this problem.