Fill celery-flower command arguments from values

[Ceridan]

There are two changes in this PR:

1. Internal port. Currently, you may change service.internalPort in Values, but flower always starts with the default port. I think it is a good idea to provide a proper port as flower command argument.
2. The broker value is hardcoded. It looks like a common practice to provide your own broker: it could be other credentials to RabbitMQ or maybe you may want to use Redis instead of RabbitMQ. I moved the broker argument to .Values.command.broker, so you may override it.