qemu: monitor: Add support for ThrottleGroup operations

qemu: monitor: Add support for ThrottleGroup operations

This change contains QMP requests for ThrottleGroup

* ThrottleGroup is updated through "qemuMonitorJSONUpdateThrottleGroup"
* ThrottleGroup is retrieved through "qemuMonitorJSONGetThrottleGroup"
* ThrottleGroup is deleted by reusing "qemuMonitorDelObject"
* ThrottleGroup is added by reusing "qemuMonitorAddObject"
* "qemuMonitorMakeThrottleGroupLimits" will be used by building qemu cmd as well

Signed-off-by: Chun Feng Wu <danielwuwy@163.com>
* change throttle group config conversions P to U allow zero.
* Apply suggested coding style changes.

Signed-off-by: Harikumar Rajkumar <harirajkumar230@gmail.com>
* Deleted all getter code.

Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>