RFR 8057149: sun/management/jmxremote/startstop/JMXStartStopTest.java fails with "Starting agent on port ... should report port in use"

[Jaroslav Bachorik]

Please, review this test change

Issue : https://bugs.openjdk.java.net/browse/JDK-8057149
Webrev: http://cr.openjdk.java.net/~jbachorik/8057149/webrev.00

The test is using 'jcmd' to start/stop the JMX agent dynamically with 
various parameters. Some of the tests use a server socket to simulate 
starting the agent with the desired port not being available. However, 
it seems that in certain situations the agent does not provide a 
conscious error message and fails with RuntimeException instead. This 
seems to be timing related and therefore the solution is to retry the 
'jcmd' command a few times with a delay to provide some cushion for the 
timing related problems.

Thanks,

-JB-