Setup autopkgtest

Description

Setup autopkgtest:

• ContinuousIntegration/autopkgtest - Debian Wiki
• Autopkgtest - Defining tests for Debian packages

Tasks

• Add an autopkgtest job. Initial work done at !98 (merged), but since there are no tests, the job is disabled.
• Create tests:
  • Smoke test: calls /usr/bin/onionprobe and checks if the command line help is displayed this does not fails. Done.
  • Tests for the other existing test cases. This may require Chutney available through an official Debian package.
• Move the smoke test upstream, directly into Onionprobe's tree.
• Re-enable the autopkgtest job.