Don't automatically install local packages

Currently the debian/test component automatically installs all locally built packages that have been indexed in the local-apt-repository. This may not be what the user wants, with a common use case being a single job to build many packages, but separate test jobs to test them.

The debian/test should probably not install anything, but continue to set up the local repository. It can then be the responsibility of the user to ensure that the correct packages are installed.