Fix client discovery crash
    
    Client discovery LDAP search assumes that the remote LDAP server will
    send an entry with lowercase attribute names. When it discovers for
    example on openldap which sends it in CamelCase, the discovery
    crashes.
    
    Convert retrieved entry to CIDict to avoid this error. Also add
    a fallback to ipa-client-install server discovery process so that
    it rather skips the faulty server instead of crashing.
    
    https://fedorahosted.org/freeipa/ticket/3446