NetworkManager not setting given DNS in resolv.conf

[d3bugg3r]

-------------------- SYSTEM INFOS ----------------
# lsb_release -rd
Description: Linux Mint 17 Qiana
Release: 17

# dpkg --list cinnamon resolvconf network-manager
ii cinnamon 2.2.16 amd64 Cinnamon desktop
ii network-manager 0.9.8.8-0ubunt amd64 network management framework (daemon and userspace tools)
ii resolvconf 1.69ubuntu1.1 all name server information handler

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So, it looks like a duplicate of https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/382161 but this was on KDE in 2009 and I doubt it would have anything to do with it...

Anyway, here is how to reproduce the problem:
- Go to network-manager settings GUI (network indicator -> Network connections)
- Edit current connection (wlan0 in my case)
- Go to IPv4 settings
- Select DHCP (addresses only)
- Set a DNS server, say 37.59.72.228 (it's the first server from OpenNIC project)
- Click save
- Click disconnect
- Click connect

In the summary, you can see the DNS server you just typed. But if you
# cat /etc/resolv.conf
then you see the DNS server provided by your DHCP server (in my case 192.168.1.1)

So the only way to bypass DHCP's DNS settings is to hard-code the DNS in /etc/resolvconf/resolv.conf.d/head

Since this can lead users to believe that they are using their favorite DNS server while they get answers from their ISP/Hotspot DNS, I checked the 'Security' box.

This could also be related to
- https://bugs.launchpad.net/ubuntu/+source/network-manager-openvpn/+bug/1072899
- https://bugs.launchpad.net/ubuntu/+source/network-manager-openvpn/+bug/1169437
- https://bugs.launchpad.net/ubuntu/+source/network-manager-openvpn/+bug/254488
- https://bugs.launchpad.net/ubuntu/+source/network-manager-openvpn/+bug/1304437