t/templates/tests: Parameterize templates for package architecture in suite 'tests'.

Use only architecture-dependent templates in the future.
Architecture-independent packages will use them with
Package-Architecture: all, which will be the default.

This change will allow the test runner to permutate through
different package architectures. Many test specifications
can accomodate 'all' and 'any', in addition to a more
explicit host architecture (although the DEB_HOST_ARCH
currently used is in doubt per #913099). Many specifications
will produce more than one test case. Together, they will
check more corner cases.