NetworkManager runs DHCP clients on CORE-generated interfaces

```
What steps will reproduce the problem?
1. Start a CORE scenario on Ubuntu 14.04, CentOS 7.0, etc.
2. Messages may pop up (CentOS 7.0) "Connection Failed: Activation of network
connection failed"
3. All virtual interfaces appear in nm-applet drop-down
4. tcpdump within CORE shows DHCP BOOTP messages and clients make requests;
potentially dozens of dhclient processes appear on the host
5. If you have the DHCP server service running, host interfaces (e.g. n3.0.234)
start receiving IP addresses (normally they have no addresses and are joined to
a bridge)

What is the expected output? What do you see instead?

We want NetworkManager to ignore CORE-generated interfaces, since CORE will
take care of assigning IP addresses.

```

Original issue reported on code.google.com by `ahrenh...@gmail.com` on 1 Aug 2014 at 2:49