Add service_provider parameter to docker::run

This module already has the code to support all systemd-based
distributions, yet it is artificially locked to just Red Hat and
Ubuntu/Debian. By exposing the service_provider parameter in the
docker::run defined type (a parameter that is also exposed in the main
docker class), this module becomes usable on most other distributions.

Other minor fixes have been added to set missing variables when running
under a non-Debian or non-RedHat operating system.