a 13.2 server, booted to kernel-default, works with auto interface naming.

re-booting to xen host

    Linux lab003 3.17.4-3.gbde0c3f-xen #1 SMP Fri Dec 5 16:20:27 UTC 2014
(bde0c3f) x86_64 x86_64 x86_64 GNU/Linux

with

    xen-4.4.1_06-342.1.x86_64

physical/ethernet devices using automated interface naming, and the bridges
that use them, are no longer brought up

    ...
    Dec 06 21:23:13 lab003 wickedd[1480]: failed to install generic settings
    Dec 06 21:23:13 lab003 ModemManager[1430]: <warn>  Couldn't find support
for device at '/sys/devices/pci0000:00/0000:00:04.0/0000:02:00.0': not
supported by any plugin
    Dec 06 21:23:13 lab003 ModemManager[1430]: <warn>  Couldn't find support
for device at '/sys/devices/pci0000:00/0000:00:06.0/0000:03:00.0': not
supported by any plugin
    Dec 06 21:23:15 lab003 kernel: Unable to read sysrq code in control/sysrq
    Dec 06 21:23:16 lab003 systemd[1]: xend.service: Supervising process 1577
which is not our child. We'll most likely not notice when it exits.
    Dec 06 21:23:16 lab003 systemd[1]: Starting Xen-watchdog - run xen watchdog
daemon...
    Dec 06 21:23:41 lab003 wicked[1495]: device brA failed: operation timed out
    Dec 06 21:23:41 lab003 wicked[1495]: device brB failed: operation timed out
    Dec 06 21:23:41 lab003 wicked[1495]: device enp3s0 failed: operation timed
out
    Dec 06 21:23:41 lab003 wicked[1495]: device enp2s0 failed: operation timed
out
    Dec 06 21:23:41 lab003 systemd-journal[801]: Forwarding to syslog missed 26
messages.
    Dec 06 21:23:41 lab003 wicked[1495]: lo              up
    Dec 06 21:23:41 lab003 wicked[1495]: brA           device-not-running
    Dec 06 21:23:41 lab003 wicked[1495]: brB           device-not-running
    Dec 06 21:23:41 lab003 wicked[1495]: enp2s0          no-device
    Dec 06 21:23:41 lab003 wicked[1495]: enp3s0          no-device
    Dec 06 21:23:41 lab003 systemd[1]: Starting Network.
    Dec 06 21:23:41 lab003 systemd[1]: Reached target Network.
    ...

the system reaches shell, but with no eth/bridge interfaces -- no external/lan
networking

disabling ifname'ing by adding to grub

    net.ifnames=0

adding a persistent udev rule

    ls -al /etc/udev/rules.d/70-persistent-net.rules 
        (empty)
    cat << EOF > /etc/udev/rules.d/70-persistent-net.rules 
    SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*",
ATTR{address}=="xx:xx:xx:xx:xx:xx", ATTR{dev_id}=="0x0", ATTR{type}=="1",
KERNEL=="eth*", NAME="eth1"
    SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*",
ATTR{address}=="yy:yy:yy:yy:yy:yy", ATTR{dev_id}=="0x0", ATTR{type}=="1",
KERNEL=="eth*", NAME="eth0"
    EOF

and renaming instances of

    enp2s0 -> eth0
    enp3s0 -> eth1

in

    /etc/sysconfig/network/*

fixes the problem; system now boots correctly, with fully functional networking

ip link
    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode
DEFAULT group default 
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master
brB state UP mode DEFAULT group default qlen 1000
        link/ether yy:yy:yy:yy:yy:yy brd ff:ff:ff:ff:ff:ff
    3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master
brA state UP mode DEFAULT group default qlen 1000
        link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
    4: brA: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP
mode DEFAULT group default 
        link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
    5: brB: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP
mode DEFAULT group default 
        link/ether yy:yy:yy:yy:yy:yy brd ff:ff:ff:ff:ff:ff