On migrating from a CentOS 6.6. to 7 server I found that if I tried to import a server in Virtualmin with its own IP, something was going wrong with the networking config. Basically the new IP would not be active, so I'd make it active via Webmin - but after reboot it was inactive again.
In case anyone else has this problem, I found that the solution is this: Although "NM_CONTROLLED=no" gets added by Webmin to the new file at /sysconfig/network-scripts/ (eg "eth0:1"), it's ALSO necessary to add that to eth0 too. (I suppose that without that, CentOS 7's network manager takes charge and the eth0:1 file (or whatever) gets igonored).