Description of problem:
Start Yumex-dnf without network connection. If metadata needs to be refreshed, yumex-dnf opens a dialog with a backtrace. Closing dialog closes also Yumex-dnf.

Version-Release number of selected component (if applicable):
yumex-dnf: 4.1.3-2.fc23 
dnfdaemon: 0.3.9-2.fc23

How reproducible:
Always

Steps to Reproduce:
1. Ensure you have no network.
2. dnf clean all
3. Run yumex-dnf

Actual results:
Dialog with backtrace:
g-io-error-quark: GDBus.Error:org.freedesktop.DBus.Python.dnf.exceptions.RepoError: Traceback (most recent call last):
  File "/usr/lib/python3.4/site-packages/dnf/repo.py", line 205, in perform
    return super(_Handle, self).perform(result)
  File "/usr/lib64/python3.4/site-packages/librepo/__init__.py", line 1425, in perform
    _librepo.Handle.perform(self, result)
librepo.LibrepoException: (8, "Cannot prepare internal mirrorlist: Curl error (6): Couldn't resolve host name for https://mirrors.fedoraproject.org/metalink?repo=updates-released-f23&arch=x86_64 [Could not resolve host: mirrors.fedoraproject.org]", 'An Curl handle error')

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.4/site-packages/dnf/repo.py", line 795, in load
    if self._try_revive():
  File "/usr/lib/python3.4/site-packages/dnf/repo.py", line 709, in _try_revive
    handle.perform()
  File "/usr/lib/python3.4/site-packages/dnf/repo.py", line 209, in perform
    raise _DetailedLibrepoError(exc, source)
dnf.repo._DetailedLibrepoError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib64/python3.4/site-packages/dbus/service.py", line 826, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "/usr/lib/python3.4/site-packages/dnfdaemon/server/__init__.py", line 83, in newFunc
    rc = func(*args, **kwargs)
  File "/usr/share/dnfdaemon/dnfdaemon-system", line 205, in SetConfig
    rc = self.set_option(setting, value)
  File "/usr/lib/python3.4/site-packages/dnfdaemon/server/__init__.py", line 696, in set_option


Expected results:
A dialog reporting network failure.