qemu.tests.qmp_command: Update the way to get qemu_binary.

After some updating, current code could not get correct qemu binary.
So Case error with message "TestNAError: Host qemu does not support qmp".

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.tests.pci_hotplug: Make device_add_nic and device_add_block have same parameters

Add a useless parameter in device_add_block().

These two function called by following code:
        try:
            # get function for adding device.
            add_fuction = local_functions["%s_%s" % (cmd_type, pci_type)]
        except Exception:
            raise error.TestError("No function for adding '%s' dev with '%s'" %
                                  (pci_type, cmd_type))
        after_add = None
        if add_fuction:
            # Do add pci device.
            after_add = add_fuction(pci_num, queues)

So they must have same parameters.
Now we meet error:
TypeError: device_add_block() takes exactly 1 argument (2 given)

Signed-off-by: Feng Yang <fyang@redhat.com>
Merge pull request #1065 from FengYang/update5

Fix for next branch - Update5