Enable support for autopkgtest

Dear Maintainer,

The submitted commits add support for autopkgtest and enable to run the testsuite automatically:

• d/tests: Add autopkgtest DEP8 tests (LP: #1679329):
  • d/t/control: New file.
  • d/t/basic-checks: Test basic configuration and version.
  • d/t/syntax-check: Perl syntax checking for the logwatch's scripts.
  • d/t/detail: Check the amount of output when using low, med and high values with the detail flag.
  • d/t/su-l-check: Check if properly report when a user become root.
    • d/t/data/su-l: Log portion used in this test.
  • d/t/apparmor-unmatched-entries : Test for not logging as unmatched some lines for apparmor audit in kern.log.
    • d/t/data/unmatched-entries-apparmor_kern.log: Log portion used in the test (LP #1577948).
  • d/t/packages-and-report: Check if the corresponding section is present into logwatch report for a list of packages/services (now only for sshd).

It has been proposed and accepted on Ubuntu [1], and you might be interested in doing the same in Debian.

Thanks in advance for considering this.

[1] https://bugs.launchpad.net/ubuntu/+source/logwatch/+bug/1679329