Always return 0 from docker init script

[cjcolvar]

Avalon-dev has been having a timing issue where both the avalon and worker containers try to run db:migrate at the same time leading to concurrent db migrate errors. When these errors occur the container stops running. I believe returning a 0 exit code from this script will allow startup to proceed and any db:migrate errors will still be logged. This isn't an issue in other environments because db:migrate isn't run automatically as part of container startup.

[cjcolvar]

Good point. That might happen but since this only affects the development environment I think the risk of that happening is less than how often the timing issue seems to be occurring so is acceptable. If it does prove to be a problem we can try another solution.