RFR 8035395: sun/management/jmxremote/startstop/JMXStartStopTest.java fails intermittently: Port already in use

[Jaroslav Bachorik]

Please, review this test fix.

Issue : https://bugs.openjdk.java.net/browse/JDK-8035395
Webrev: http://cr.openjdk.java.net/~jbachorik/8035395/webrev.00

Currently, the test is using two fixed ports to start JMX connector and 
RMI registry when necessary. It can not deal with situations when the 
ports are not available. The patch is adding the ability to obtain ports 
from the ephemeral range and use them instead of the hardcoded ones. It 
also tries to minimize the chance of another process stealing the ports 
by holding the corresponding SocketServers open till right before the 
port is actually needed.

Thanks,

-JB-