parallels: delete old networks in prlsdkDoApplyConfig before adding new ones

parallels: delete old networks in prlsdkDoApplyConfig before adding new ones

In order to change an existing domain we delete all existing devices and add
new from scratch. In case of network devices we should also delete corresponding
virtual networks (if any) before removing actual devices from xml. In the patch,
we do it by extending prlsdkDoApplyConfig with a new parameter, which stands for
old xml, and calling prlsdkDelNet every time old xml is specified.

Signed-off-by: Maxim Nestratov <mnestratov@parallels.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>