RFR: Backport of JDK-8044135: Add API to start JMX agent from attach framework

[Staffan Larsen]

This is a review for a backport of JDK-8044135 to jdk8u. This fix had a few dependencies that also needed backporting, so included in this review are the following fixes from JDK9:

• 8044135 Add API to start JMX agent from attach framework (jdk)
• 8039173 Propagate errors from Diagnostic Commands as exceptions in the attach framework (jdk)
• 8044398 Attach code should propagate errors in Diagnostic Commands as errors  (hotspot)

The only significant change from the version in JDK 9 is that startManagementAgent() and startLocalManagementAgent() in VirtualMachine.java have "@since 1.8" (instead of 1.9).

After speaking with the maintainers and gatekeepers, I plan to push this to the jdk8u-hs-dev repository.

Thanks,
/Staffan