Since commit f14c37, virDomainConfVMNWFilterTeardown is reporting errors
thus any previously reported error gets overwritten.
We need to save the errors in qemuDomainAttachNetDevice before calling
this function when we are in cleanup code.

https://bugzilla.redhat.com/show_bug.cgi?id=1598311Signed-off-by: NKaterina Koukiou <kkoukiou@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>