Fix non persistent network handling (backend)

If some network is not persistent and the user tries to stop it, it is
going to be removed by libvirt and causes an error in Kimchi.
This patch changes the backend in order to get persistent information.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
Fix non persistent network handling (frontend)

If some network is not persistent and the user tries to stop it, it
is going to be removed by libvirt and causes an error in Kimchi.
This patch warns the user with a message in the ui about the situation,
avoinding mistakes.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>
Fix non persistent network handling (mockmodel/tests)

This patch adds the persistent information to mock model and tests to
check if it is true.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>