downstream: Add ability to use different jira instances
    
    There are a few changes in this patch set. First we'd like to
    support different github/pagure repos being able to be synced
    with different instances of JIRA. We currently have two within
    Red Hat that we are using, but this strategy should also support
    more than two. Summary of changes in this patch:
    
    - add support for multiple jira instances to the config under the
      **config['sync2jira']['jira'] config location. For example if I
      wanted to grab the auth info for the pnt-jira I would access
      **config['sync2jira']['jira']['pnt-jira'].
    - add support for a 'default_jira_instance' config key that allows
      for a user to specify which jira in the jira dict to use as a default
      in case config entries don't specify a jira instance to use.
    - switch function names from functions that that are only called in
      this file to have a preceding underscore (func -> _func)
    - make the only functions that get called from outside this file to
      be the ones that create a client connection to the jira instance
    - pass the jira client object around to the private functions