'Read replication devices from configuration
Several replication devices are permitted.
If an entry already exists an error is assumed.
The format is:
replication_device = backend_id:vendor-id-1,unique_key:val....'

@_trace_time
def _read_replication_devices(self):

    if (not self.driver):
        return
    replication_devices = self._get_safely_from_configuration('replication_device', default={})
    if (not replication_devices):
        LOG.debug('No    replication    devices    were    found')
    for dev in replication_devices:
        LOG.debug('Replication    device    found:    %(dev)s', {'dev': dev})
        backend_id = dev.get('backend_id', None)
        if (backend_id is None):
            LOG.error('Replication    is    missing    backend_id:    %(dev)s', {'dev': dev})
        elif self.targets.get(backend_id, None):
            LOG.error('Multiple    entries    for    replication    %(dev)s', {'dev': dev})
        else:
            self.targets[backend_id] = {}
            device = self.targets[backend_id]
            for (k, v) in dev.iteritems():
                if (k != 'backend_id'):
                    device[k] = v
