test: move sequential/test-debug-port-cluster

Move sequential/test-debug-port-cluster to test/parallel.  This test
is safe to run in parallel with other debugger tests, it doesn't use
fixed port numbers.

PR-URL: https://github.com/iojs/io.js/pull/306
Reviewed-By: Miroslav Bajtoš <miroslav@strongloop.com>

diff --git a/test/sequential/test-debug-port-cluster.js b/test/parallel/test-debug-port-cluster.js
similarity index 100%
rename from test/sequential/test-debug-port-cluster.js
rename to test/parallel/test-debug-port-cluster.js