Store system test output in bin/tests/system/

Store system test output in bin/tests/system/

Some clean.sh scripts contain overly broad file deletion wildcards which
cause the test.output file (used by the system test framework for
collecting output) in a given system test's directory to be erroneously
removed immediately after the test is started (due to setup.sh scripts
calling clean.sh at the beginning).  This prevents the test's output
from being placed in bin/tests/system/systests.output at the end of a
test suite run and thus can lead to test failures being ignored.  Fix by
storing each test's output in a test.output.<test-name> file in
bin/tests/system/, which prevents clean.sh scripts from removing it (as
they should only ever affect files contained in a given system test's
directory).