jmx-dev RFR 8034177: sun/management/jmxremote/startstop/JMXStartStopTest.java should report port in use

[Jaroslav Bachorik]

Please, review this test change.

Issue : https://bugs.openjdk.java.net/browse/JDK-8034177
Webrev: http://cr.openjdk.java.net/~jbachorik/8034177/webrev.00

The test is currently using a well-known SSH port 22 to make sure it is 
not possible to start the management agent on this port. However, this 
may fail when SSH server is not running on a test machine.

The fix adds the possibility to to start up a dummy socket server in the 
tested application and use the port from that socket server to make sure 
that the management agent refuses to start on that port.

Thanks,

-JB-