qemuBuildControllerPCIDevStr: Format via JSON properties

qemuBuildControllerPCIDevStr: Format via JSON properties

Internally format the PCI controller properties into JSON, but convert
it back to a string so that we for now change just the SCSI controller.

The change in tests is expected as the 'port' field for various PCI
controllers is expected to be a number and thus can't be represented as
a hexadecimal value in JSON.

QEMU expects the following types:

'pci-bridge'
  chassis_nr=<uint8>     -  (default: 0)

'pxb-pcie':
  bus_nr=<uint8>         -  (default: 0)

'pcie-root-port'
  port=<uint8>           -  (default: 0)
  chassis=<uint8>        -  (default: 0)
  hotplug=<bool>         -  (default: true)

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