testsuite: automatize generation of dependencies for tests

testsuite: automatize generation of dependencies for tests

* tests/gen-test-deps: New script, automatically generates
dependencies for the tests.
* tests/Makefile.am (EXTRA_DIST): Distribute it.
($(srcdir)/tests-deps.am): New rule.
(include $(srcdir)/tests-deps.am): New inclusion.
Remove hand-written dependencies for tests.  Other related
updates.
* tests/list-of-tests (tap_with_common_setup_TESTS,
tap_other_TESTS): Delete, their content merged back into ...
(handwritten_TESTS): ... this.
* tests/.gitignore (tests-deps.am): New ignored file.
* bootstrap: Generate `tests/tests-deps.am'.