packaging: use wildcard for test files in Debian

we can also use test_* instead of listing all test_xx  files while
building debian package

Reviewed-by: Ken Dreyer <ken.dreyer@inktank.com>
Merge pull request #1371 from ceph/wip-debian-files

packaging: use wildcard for test files in Debian

Reviewed-by: Sage Weil <sage@inktank.com>