Add .test-{autopkgtest,piuparts}-stretch template jobs

See https://salsa.debian.org/samba-team/samba/-/jobs/112077:

The following packages have unmet dependencies:
 python-samba : Depends: python-ldb (>= 1.1.2~) but it is not going to be installed
                Depends: libldb1 (>= 0.9.21) but it is not going to be installed
                Depends: samba-libs (= 2:4.5.16+dfsg-1) but it is not going to be installed

I think autopkgtest is the most important, then piuparts then reprotest.

Edited Jan 20, 2019 by Mathieu Parent

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