add unicorn_init.sh

unicorn_init.sh should be able to read APP_ROOT/config/unicorn.rb and
/etc/unicorn/APP_NAME.conf and control unicorn
Merge pull request #2226 from workmaster2n/unicorn_init

add unicorn_init.sh
supress unicorn init.d kill messages, update #2226
updagte the readme part of unicorn init.d script, update #2226
add handling of user/root in unicorn init.d script
fix detecting user in unicorn init.d script, improve error reporting