This change allows operators to specify a DOCKER_BIN environment variable. This will specify a binary to run when executing docker, which is useful in cases where the 'docker' command being run must be modified in a way that would otherwise be invasive to Dokku, but minimalistic if done within a wrapper.
While I do not agree with _every_ style change, this will force Dokku to have consistent formatting across all shell scripts, which is arguably a Good Thing™.
The command used to reprocess everything is:
```shell
shfmt -l -bn -ci -i 2 -w .
```
Some systems - such as a mounted read-only CIFS filesystem - do not fully support chown, and chowning should be considered optional for cases when the host os has already taken care of permissioning. This commit allows users to disable chown by setting a property on the scheduler-docker-local plugin.
