qemu_migration: check for interface type 'hostdev'

qemu_migration: check for interface type 'hostdev'

When we try to migrate vm, we check if it contains only devices
that are able to migrate. If a hostdev device is not able to
migrate we raise an error with <hostdev/>, but it can actually be
<interface/>, so we need to check if hostdev device was created
by us from interface and show the right error message.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1942315

Signed-off-by: Kristina Hanicova <khanicov@redhat.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>