Fix ipa-dns-install
    
    When DNS plugin is installed via ipa-dns-install and user has a valid
    Kerberos ticket at the time, the DNS installation is corrupt and named
    won't start, reporting Preauthentication error.
    
    When the non-DM identity is used for authentication, krbprincipalkey
    attribute in DNS service LDAP record is not created, thus leading
    to the error. This patch makes sure that authentication with Directory
    Manager password is used every time.
    
    https://fedorahosted.org/freeipa/ticket/1483