Cleanup isolated AptGet and Redis services

Because they are isolated, we can replace self.hosts with self.host.
AptGet utilities: is_package_available and setup

setup() is used in many other services but not here. Added as a shortcut to
setup the extra sources and install the package.

is_package_available will tell you whether the package is listed in the
installed sources, or whether you will need an extra one.
Merge pull request #7 from janfabry/cleanup/hosts

Cleanup isolated AptGet and Redis services