Make ipa 2.2 client capable of joining an older server
    
    IPA server of version 2.2 and higher supports Kerberos S4U2Proxy
    delegation, i.e. ipa command no longer forwards Kerberos TGT to the
    server during authentication. However, when IPA client of version
    2.2 and higher tries to join an older IPA server, the installer
    crashes because the pre-2.2 server expects the TGT to be forwarded.
    
    This patch adds a fallback to ipa-client-install which would detect
    this situation and tries connecting with TGT forwarding enabled
    again. User is informed about this incompatibility.
    
    Missing realm was also added to keytab kinit as it was reported to
    fix occasional install issues.
    
    https://fedorahosted.org/freeipa/ticket/2697