migrate tests from bin/tests/dnssec-signzone to bin/tests/system/dnssec

migrate tests from bin/tests/dnssec-signzone to bin/tests/system/dnssec

- added tests to the dnssec system test that duplicate the ones
  from bin/tests/dnssec-signzone
- changed cleanall.sh so it doesn't automatically remove all
  key files, because there are now some of those that are part of the
  distribution

(cherry picked from commit ccfe778c0165dc26ab5ac5291e5ab53f9d0a3298)
(cherry picked from commit d8f8eee381497d97d0bd0c013aafef2cfd674b2d)
(cherry picked from commit dbb225d83eba5f883a78cb571b931fc3c4ec1ce0)
(cherry picked from commit 161f525942d5a07d46063d66b53efe3963ce1990)