Really remove NetworkManager from CentOS 7
Really remove NetworkManager from CentOS 7

And include some other enhancements from the official CentOS 7
cloud image
https://github.com/CentOS/sig-cloud-instance-build/blob/master/cloudimg/CentOS-7-x86_64-GenericCloud-201606-r1.ks

Change-Id: Ia246f9908f2a405e5d8defa79f1dc7ba9fec47d6

NeCTAR-RC/nectar-images,NeCTAR-RC/nectar-images