Improve logging and error handling in DB initialization

- Log4j is now used for logging DB initialization
- All forked postgresql commands now have their stdout and
  stderr logged
- Forked commands are logged in a form which can be copied and pasted
  into a shell for debugging
- Failure in any step of the initialization is raised as a
  RuntimeException, which forces a nonzero exit
- Database logs are now placed in euca.log.dir

Fixes EUCA-3334