QPID-6284: [Java Broker Tests] Add system test demonstrating the effect of using SSL on a connection.

* VaryingNumberOfParticipants x axis extended to 20 participants as on current test hardware, existing maximum
  parameter (10) did not show the point at which returns begin to diminish.
* Cloned VaryingNumberOfParticipants for the SSL test.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1647521 13f79535-47bb-0310-9956-ffa450edef68