Description of problem:

Try to register oVirt-Engine from the oVirt Node, vdsm-reg will complain about vdsm-rest not installed, from vdsm.reg log:

"Unable to load the rest  server module. Please make sure it is installed."

Reference:
http://www.mail-archive.com/users@ovirt.org/msg02005.html

Caused by:

vdsm/clientIF.py:
  if config.getboolean('vars', 'rest_enable'):
            try:
                self._loadBindingREST()
            except ImportError:
                self.log.error('Unable to load the rest server module. '
                               'Please make sure it is installed.')

Talked with aglitke, we are going to move to a warning message.