In order to install a package from jessie-backports, apt-get has to be told
to get it from there rather than the main archive. It will not use
jessie-backports by default even if it is added as an apt source.
closes#224
This does not have the careful result rechecking that chef has, when it
installs each package in the list one at a time. So to help with failures
caused by a package failing to download, first try downloading all the
package, then run the install. The install pass will try to download any
missing packages.
Really, this should use ansible or perhaps chef again since those include
lots of tricks around this stuff.
This makes it so there is only a single `apt-get install` command run,
instead of one command per-package like with the chef script. It also adds
`apt-get upgrade` to make sure that the base box is fully up-to-date.
