move the db seeding outside the django container_init script

seeding is now performed by the bootstrap script directly (except called
with --noseed). It consists of two parts:
 - seeding the db: with 3 users (admin@localhost, devel@localhots and
   user@localhost) and one webapp ('sleep' that has 1 version 'latest')
 - seeding the registry with one image: "localhost/sleep:latest" for the
   sleep webapp