RFR: 8044135 Add API to start JMX agent from attach framework

[Staffan Larsen]

This is the first part in a two-part series of removing the management-agent.jar and replacing its functionality with APIs in the attach framework. In this change I have added the new APIs, a later change will remove management-api.jar.

management-agent.jar is the java agent that is used with the attach API to start the JMX agent in a target VM. It's the approach used in JDK 6 to start JMX in a running VM and predates the "jcmd ManagementAgent.start" command added in 7uX.
 
management-agent.jar will be problematic when we move to a modular JDK in JDK 9 and should be replaced by a "real" API. So this change adds two methods to VirtualMachine in the attach framework for starting either a local or a remote management agent.

webrev: http://cr.openjdk.java.net/~sla/8044135/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8044135

Thanks,
/Staffan