Autopkgtests for the rsync package

Description of the project: A recent series of breakages caused in the rsync package as part of CVE fixes exposed the lack of testing coverage on Debian, e.g.: https://github.com/RsyncProject/rsync/issues/702. The rsync package on Debian has a single autopkgtest which only runs upstream's tests. This project is for adding end-to-end tests to the rsync package, covering as many usecases as possible, making impossible for regressions to go unnoticed. These tests will also be submitted to stable through the proposed-updates mechanism.