Description of problem:
It is possible to set empty profile to vm network, in this case the network can't attached to VM.

Version-Release number of selected component (if applicable):
rhevm-3.3.0-0.21.master.el6ev.noarch

How reproducible:
100%

Steps to Reproduce:
1. Create new network
2. Edit the network to non-vm
3. set the network back to vm network

Actual results:
VM network have no profile

Expected results:
The operation should blocked if profile name is empty

Additional info:
When updating network to non-vm the profile for that network deleted, but when updating the network to VM network no new profile is created and the user need to create it from the profile tab in the edit network window.