Add script to release slapos.cookbook

This script everything required to release slapos.cookbook, and verbose additional information to
the user review and push the changes.

This script automatically slapos.cookbook version on update stack/slapos.cfg also, if you want only
release the EGG w/o using it, you can call it using:

 EGG_ONLY=Y bash release-cookbook

else, call it only by 'bash release-cookbook'.