allow users to pass subrelease and relserver for the same release
allow users to pass subrelease and relserver for the same release

Change-Id: I2ed88ae2c4241f57aa32607353e68072464a20d1
Reviewed-on: http://review.couchbase.org/119462
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Bo-Chun Wang <bb86fd206c9c35341feb9b50e74a74a83e254d63@couchbase.com>

couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner