I am using the Newest xUbuntu 14.04 Trusty Tahrir [or however you spell it] or this will work in ANY Ubuntu version or Flavor with or without network manager [UGH, that Network Manager software is a real pain compared to the interfaces definitions file IMHO].
Wouldn't you just sudo apt-get purge network manager and go ahead and use /etc/network/interfaces anyways? It is there and once you manually specify [or not if you issue ifup [may need to use ifup -a (means all adapters) or possibly ifup after purging net manager it should reach out to DHCP and grab an address].
I use OpenVPN and have to as part of that use /etc/network/interfaces to manually specify my bridge connection and it's options. Once you define [the default file should just go for DHCP without modification] your connections using the interfaces file you can just issue ifdown -a or ifup -a to disconnect and then reconnect to network after any modifications without restarting the machine.
Last once you use the interfaces file network manager will appear greyed out in the notification area. This is normal you are no longer using Network Manager you are using ifup and ifdown.
And yes this is related to ifconfig so if you use ifconfig in terminal then you are already used to this system and have used it to view adapter info already ifconfig is part of the same package as ifdown and ifup and should be fully present and ready to go even from a fresh install you don't need to apt-get install anything for this to be usable.
Viola follow any /etc/network/interfaces directions needed and they work [and you get rid of a small annoying piece of software [If you google net manager you see people getting disconnected/reconnected randomly and other misc issues]. If you know how to handle the interfaces file this is FAR more easy AND WAY MORE STABLE [and not hard to learn, only took me roughly 30 min to iron out advanced options like setting the default DNS search domains, enabling promiscuous mode, etc] :-D
Hope that helps.