Did you try CentOS 7 Workstation with "Development tools" && "Virtualization" ?
I never saw error you talking about. When I am done with Juno install && Editing ifcfg-br-ex, ifcfg-enp2s0 :-

chkconfig network on
systemctl stop NetworkManager
systemctl disable NetworkManager
service network restart

Syntax of ifcfg-* files is like on old CentOS 6.X ( DEVICE="enp2s0" not NAME="enp2s0")
It might happen that reboot required to start network service on Fedoras 21,20, but not on CentOS 7
Here it works right away.

[root@juno1 network-scripts(keystone_admin)]# cat ifcfg-br-ex
DEVICE="br-ex"
BOOTPROTO="static"
IPADDR="192.168.1.127"
NETMASK="255.255.255.0"
DNS1="83.221.202.254"
BROADCAST="192.168.1.255"
GATEWAY="192.168.1.1"
NM_CONTROLLED="no"
DEFROUTE="yes"
IPV4_FAILURE_FATAL="yes"
IPV6INIT=no
ONBOOT="yes"
TYPE="OVSIntPort"
OVS_BRIDGE=br-ex
DEVICETYPE="ovs"

[root@juno1 network-scripts(keystone_admin)]# cat ifcfg-enp2s0
DEVICE="enp2s0"
# HWADDR=00:22:15:63:E4:E2
ONBOOT="yes"
TYPE="OVSPort"
DEVICETYPE="ovs"
OVS_BRIDGE=br-ex
NM_CONTROLLED=no
IPV6INIT=no