Improve DN usage in ipa-client-install
    
    A hotfix pushed in a scope of ticket 3088 forced conversion of DN
    object (baseDN) in IPA client discovery so that ipa-client-install
    does not crash when creating an IPA default.conf. Since this is not
    a preferred way to handle DN objects, improve its usage:
    
    - make sure, that baseDN retrieved by client discovery is always
      a DN object
    - update ipachangeconf.py code to handle strings better and instead
      of concatenating objects, make sure they are converted to string
      first
    
    As a side-effect of ipachangeconf changes, default.conf config file
    generated by ipa-client-install has no longer empty new line at the
    end of a file.
    
    Whole ipachangeconf.py has been modified to be compliant with PEP8.
    
    https://fedorahosted.org/freeipa/ticket/3088