RFR: 6696975: JTop plugin fails if connected readonly to target JVM

[Erik Gahlin]

Please review this change.

ThreadMXBean#setThreadCpuTimeEnabled(true) assumes read-write access to 
the underlying JVM, but if read-access is only available plug-in will 
fail and throw an exception.
http://monaco.us.oracle.com/detail.jsf?cr=6696975

Unexpected exceptions occurring in JConsole are taken care of by 
6696970, but plug-in should still handle read-only access gracefully, as 
it today does if functionality is not supported by JVM. This can be 
important if plug-in is used by other programs.

Webrev:
http://cr.openjdk.java.net/~egahlin/6696975/

A sponsor is needed

Thanks
Erik