RFR 8075926: Add a sun.management.JMXConnectorServer perf counter to track its state

[Jaroslav Bachorik]

Please, review the following change

Issue : https://bugs.openjdk.java.net/browse/JDK-8075926
Webrev: http://cr.openjdk.java.net/~jbachorik/8075926/webrev.00

The sun.management.JMXConnectorServer.<version>.<key> perf counters are 
not updated when the remote management agent is stopped.

The perf counters show stale data and mislead the users.

Since it is not possible to 'un-export' perf counters we need an 
additional counter tracking the version of the related perf counters in use.

In the current implementation each start of the remote management agent 
will export a new set of the related perf counters 
(sun.management.JMXConnectorServer.<version>.<key>) with the <version> 
part increased by one. The first remote management agent start will use 
0 as its version.

The new counter 'sun.management.JMXConnectorServer.remote' will have 
value of -1 if the remote management is stopped and non-negative number 
corresponding to the version of the related perf counters in use.

Thanks,

-JB-