Do not raise exception if Jenkins API is not available

Avoid the following exception if Jenkins is not installed yet:

  [CRITICAL] Failed to load grains defined
  ...
  JenkinsException: Error in request: [Errno 111] Connection refused

Change-Id: Id849375a14fd7a928b64979b92620aa37041dc9d
Closes-Bug: https://mirantis.jira.com/browse/PROD-17822
1 file changed