Add qemuMonitorJSONGetObjectProperty() method for QMP qom-get command

Add qemuMonitorJSONGetObjectProperty() method for QMP qom-get command

Add a new qemuMonitorJSONGetObjectProperty() method to support invocation
of the 'qom-get' JSON monitor command with a provided path, property, and
expected data type return. The qemuMonitorJSONObjectProperty is similar to
virTypedParameter; however, a future patch will extend it a bit to include
a void pointer to balloon driver statistic data.

NOTE: The ObjectProperty structures and API are added only for the
      purpose of the qemumonitorjsontest

The provided test will execute a qom-get on "/machine/i440fx" which will
return a property "realized".