Description of problem:
RuntimeError(_("Hostname is required")) cannot be triggered

Version-Release number of selected component (if applicable):
virt-manager-1.4.3-3.el7.noarch

How reproducible:
100%

Steps to Reproduce:
1. Click 'Add Pool' button in virt-manager.
2. Select netfs pool type and set any pool name for it.
3. click 'Forward'.
4. Leave 'Host Name' and 'Source Path' as blank, then click 'Finish'.

Actual results:
Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/createpool.py", line 395, in forward
    if self.validate(notebook.get_current_page()) is not True:
  File "/usr/share/virt-manager/virtManager/createpool.py", line 547, in validate
    return self._validate_page_format()
  File "/usr/share/virt-manager/virtManager/createpool.py", line 527, in _validate_page_format
    self._pool.validate()
  File "/usr/share/virt-manager/virtinst/storage.py", line 509, in validate
    raise RuntimeError(_("Source path is required"))
RuntimeError: Source path is required


Expected results:
RuntimeError(_("Hostname is required"))

Additional info:
Should argument be "hosts" instead of "host"?

    def validate(self):
        if self.supports_property("host") and not self.hosts:
            raise RuntimeError(_("Hostname is required"))