Hello,
I have updated one test environment to 4.2 (it was in 4.1.9)
I have a guest in Oracle Linux 6 and epel 6 repo enabled.
After powering down and start the VM, I saw the exclamation mark regarding ovirt-guest-agent latest version needed.

On the VM the process was dead and I took the time of updatng it 
from ovirt-guest-agent-1.0.12-4.el6.noarch
to ovirt-guest-agent-1.0.13-2.el6.noarch

and start the agent.
All seems ok; no exclamation mark now and I see the ip addresses of the guest in 4.2 web admin gui.

But in log of ovirt-guest-agent I see:

MainThread::ERROR::2018-05-28 14:34:55,711::ovirt-guest-agent::140::root::Unhandled exception in oVirt guest agent!
Traceback (most recent call last):
  File "/usr/share/ovirt-guest-agent/ovirt-guest-agent.py", line 134, in <module>
    agent.run(daemon, pidfile)
  File "/usr/share/ovirt-guest-agent/ovirt-guest-agent.py", line 65, in run
    self.agent = LinuxVdsAgent(config)
  File "/usr/share/ovirt-guest-agent/GuestAgentLinux2.py", line 466, in __init__
    AgentLogicBase.__init__(self, config)
  File "/usr/share/ovirt-guest-agent/OVirtAgentLogic.py", line 188, in __init__
    self.vio = VirtIoChannel(config.get("virtio", "device"))
  File "/usr/share/ovirt-guest-agent/VirtIoChannel.py", line 151, in __init__
    self._stream = VirtIoStream(vport_name)
  File "/usr/share/ovirt-guest-agent/VirtIoChannel.py", line 132, in __init__
    self._vport = os.open(vport_name, os.O_RDWR)
OSError: [Errno 2] No such file or directory: '/dev/virtio-ports/com.redhat.rhevm.vdsm'
MainThread::INFO::2018-05-28 14:42:45,535::ovirt-guest-agent::59::root::Starting oVirt guest agent

The status of files under the indicated directory is:

# ll /dev/virtio-ports/
total 0
lrwxrwxrwx 1 root root 11 May 28 14:34 com.redhat.spice.0 -> ../vport0p3
lrwxrwxrwx 1 root root 11 May 28 14:34 org.qemu.guest_agent.0 -> ../vport0p2
lrwxrwxrwx 1 root root 11 May 28 14:42 ovirt-guest-agent.0 -> ../vport0p1

Anything to be done at my side at guest/host configuration level?

Thanks,
Gianluca