Change erts/etc/unix/Install.src to explicitly set exit code to 0 at the end of the script

[Kenji Rikitake]

git fetch git://github.com/jj1bdx/otp.git r13b03_installsrc_exitcode

Change erts/etc/unix/Install.src to explicitly set exit code to 0 at the 
end of the script

This patch will ensure the Install.src script to exit with the exit code
0 when the execution finished at the end of the script.  

Originally from FreeBSD port patch.

Regards,
Kenji Rikitake