Preload and never shutdown one instance and increase timeout

First access to Foreman instance can be slow, particularly when there are many
plugins installed (e.g. Katello). This patch preloads the first worker instance
at the very beginning when passenger is started, so there is almost no delay.

If you like it, I am happy to parametrize it. I would love to see this as a
default value.
I agree with @iNecas that
```erb
<%= @passenger_min_instances %>
<%= @passenger_start_timeout %>
```
would be cleaner.