Generate proper bridge port configuration

bnc#879617

* Removed workaround for sysconfig (0.0.0.0/32).
* Huge cleanup.
* Updates for testsuite
really not DRY. Better to have
```
describe Yast::LanItems do
  before(:each) do
    @lan_items = Yast::LanItems
    @lan_items.main
    @lan_items.Items = deep_copy(MOCKED_ITEMS)
  end
  
  describe ".FindAndSelect" do
    ...
```