Updated test harness to generate unique IDs for simulatenous
runs on the same machine.

Change-Id: I0361ff5d85e3b0a05e3843b9665c0c73b3feffa4
Reviewed-on: http://review.couchbase.org/30164
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Brett Lawson <brett19@gmail.com>