Freight Support

I've added basic Freight support to jenkins-debian-glue. Currently there is still a bug in Freight, which I'm about to report them upstream.

The basic idea behind this, is to have a way to keep multiple versions of packages in a repository and to circumvent reprepo's shortcomings.

There are a couple of new options which can be configured to build-and-provide-package:

```REPOS```: This will have the same effect on Freight as it would have with reprepro.

```FREIGHT_BASE```: The base directory for Freight storage. Set this to use a custom directory structure for Freight. Read the description for ```FREIGHT_REPOSITORY``` and figure a value of *default* for it.
The default is empty and use the system wide configuration. This includes */etc/freight.conf*, */var/lib/freight* for the package archive and */var/cache/freight* for the package cache. 

```FREIGHT_REPOSITORY```: A name for the repository managed by freight. It  will create an additional directory for abstraction. Specifying 'infrastructure' as value will create the following directory structure:
* /srv/freight/infrastructure-source .. Freight package archive.
* /srv/freight/infrastructure .. Freight package cache.
* /srv/freight/infrastructure.conf .. A separate Freight configuration file.