Provide support for Debian; to uninstall docker and deps

I have successfully tested the uninstall functionality (by setting $docker::params::ensure to 'purged').  These changes will purge, or supposedly absent docker (and its dependent packages).  Restoring the ::ensure value to 'present' restores the installation successfully.  I made no attempt to remove the /etc/apt/sources.list.d/docker.list file nor to purge the apt key, although it seems those two actions would be appropriate if ::ensure is set to 'purged'.  That is work for a later day.  This functionality was sufficient for running the tests necessary for my work on the feature I am interested in.  

I failed to find an init.d script upon reinstall.  I am unsure whether that means that no such script exists in the package, or if my conditional wrapper has a bug in it.  I will investigate that further after lunch, perhaps.  Still need to sort out how to start the docker service on a debian server.  

I manually added in:
https://github.com/dotcloud/docker/blob/master/contrib/init/sysvinit-debian/docker 

modifying it to ensure that it runs under bash, rather than dash.  Should probably contribute that patch upstream.  
https://github.com/dotcloud/docker/issues/7031

When that file is incorporated into the docker package, it should be unnecessary to include it here as an explicit File['/etc/init.d/docker'] resource.  After some testing I am confident that these changes should successfully ensure => running, enable => true, starting the daemon and populating /etc/rc?.d/*docker.  

At this point this PR should resolve https://github.com/garethr/garethr-docker/issues/75 and provide useful support for debian servers.  

I just added support for the installation and removal of recommended packages, which right now includes only bridge-utils on debian/ubuntu machines.  This has been manually tested and found to work, for $docker::params::ensure_recommended being 'present' or 'purged'.  

If the Tavis CI server is satisfied, I am now recommending that these changes be exercised with the maintainer's regression suite and merged into the source project.  

TODO:  

* I have made no attempt to cover these changes in the tests.  But yesterdays work (in docker::install) to allow for purging the package permitted me to adequately test this functionality manually.  

* The docker::install manifest purges the /etc/init.d/docker and /etc/rc?.d/*docker files appropriately, but it still leaves /etc/default/docker and any other configuration files alone.