Description of problem:

During creation of a new VM with virt-manager, I always have an error message when selecting the default device storage or adding a new storage device.

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1. Create a new VM named "testVM"
2. During creation, when you have the screen in order to choose network, choose customize configuration before installation (in french version "Personnalisation la configuration avant l'installation")
3. You are now on screen "testVM virtual machine" where you can choose to add or remove hardware before you can lauch the creation of the VM. When you click on "Disk 1", which is the default created disk, you have a popup window with an error message :

Erreur lors de l'actualisation de la page du matériel : unsupported operand type(s) for /: 'NoneType' and 'int'


(sorry I have the french version, which can be translated by 
"Error during updating the hardware page")


Erreur lors de l'actualisation de la page du matériel : unsupported operand type(s) for /: 'NoneType' and 'int'

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/details.py", line 1307, in hw_selected
    self.refresh_disk_page()
  File "/usr/share/virt-manager/virtManager/details.py", line 2905, in refresh_disk_page
    iotune_read_bytes_sec = disk.iotune_read_bytes_sec / 1024
TypeError: unsupported operand type(s) for /: 'NoneType' and 'int'



Reproducible: 

Steps to Reproduce: