[vmware plugin] subdevices w/o MAC addresses shouldn't be included in scan results.

At the current shape of the scan results form, there's no way to save subdevices w/o MAC addresses detected by vmware plugin. And since such situation is relatively rare (i.e. it seems to be limited only to some specific appliances), we have decided to exclude them from scan results. Instead of that, a suitable message will be presented to the user in scan logs. 

As a bonus, I've fixed some typos here and there ;)