vlan: fix format string for 1000 bridges/vlans test

Fix the following:

  Traceback (most recent call last):
    File "/usr/local/lib/python3.6/site-packages/behave/model.py", line 1329, in run
      match.run(runner.context)
    File "/usr/local/lib/python3.6/site-packages/behave/matchers.py", line 98, in run
      self.func(context, *args, **kwargs)
    File "features/steps/connection.py", line 378, in add_bridges_vlans_range
      'add connection %s failed: %s' % (result['error'])
  TypeError: not enough arguments for format string
5 jobs for !858 with bg/assert-fmt-str in 6 minutes and 55 seconds
latest detached
Status Name Job ID Coverage
  Test
passed TestResults #14911826
manual

00:05:38

passed UnitTests #14911825

00:01:17

 
  External
failed https://desktopqe-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/beaker-NetworkManager-gitlab-trigger-test-upstream/1960/

passed https://jenkins-networkmanager.apps.ocp.ci.centos.org/job/NetworkManager-test-mr/771/

06:24:37

failed https://desktopqe-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/beaker-NetworkManager-gitlab-trigger-test-upstream/1960/

00:07:17