qemumonitorjsontest: Test qemuMonitorJSONSystemPowerdown
qemumonitorjsontest: Test qemuMonitorJSONSystemPowerdown

Right now, we are testing qemuMonitorSystemPowerdown instead of
qemuMonitorJSONSystemPowerdown. It makes no harm, as both functions have
the same header and the former is just a wrapper over the latter. But we
should be consistent as we're testing the JSON functions only in here.

taget/libvirt,rlaager/libvirt,nertpinx/libvirt,shugaoye/libvirt,fabianfreyer/libvirt,cbosdo/libvirt,andreabolognani/libvirt,zippy2/libvirt,zhlcindy/libvirt-1.1.4-maintain,eskultety/libvirt,olafhering/libvirt,cbosdo/libvirt,agx/libvirt,jfehlig/libvirt,libvirt/libvirt,crobinso/libvirt,agx/libvirt,taget/libvirt,fabianfreyer/libvirt,olafhering/libvirt,jardasgit/libvirt,olafhering/libvirt,nertpinx/libvirt,elmarco/libvirt,VenkatDatta/libvirt,eskultety/libvirt,fabianfreyer/libvirt,zhlcindy/libvirt-1.1.4-maintain,shugaoye/libvirt,libvirt/libvirt,andreabolognani/libvirt,crobinso/libvirt,rlaager/libvirt,nertpinx/libvirt,crobinso/libvirt,eskultety/libvirt,rlaager/libvirt,nertpinx/libvirt,zippy2/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,agx/libvirt,elmarco/libvirt,elmarco/libvirt,taget/libvirt,datto/libvirt,zhlcindy/libvirt-1.1.4-maintain,agx/libvirt,andreabolognani/libvirt,cbosdo/libvirt,jardasgit/libvirt,olafhering/libvirt,libvirt/libvirt,zhlcindy/libvirt-1.1.4-maintain,cbosdo/libvirt,nertpinx/libvirt,eskultety/libvirt,fabianfreyer/libvirt,zippy2/libvirt,jardasgit/libvirt,jfehlig/libvirt,datto/libvirt,taget/libvirt,datto/libvirt,libvirt/libvirt,crobinso/libvirt,jardasgit/libvirt,elmarco/libvirt,andreabolognani/libvirt,zhlcindy/libvirt-1.1.4-maintain,eskultety/libvirt,VenkatDatta/libvirt,datto/libvirt,shugaoye/libvirt,VenkatDatta/libvirt,elmarco/libvirt,shugaoye/libvirt,andreabolognani/libvirt,rlaager/libvirt,VenkatDatta/libvirt,agx/libvirt,datto/libvirt,cbosdo/libvirt,jardasgit/libvirt,rlaager/libvirt,VenkatDatta/libvirt,zippy2/libvirt,shugaoye/libvirt,jfehlig/libvirt,taget/libvirt