ipa-adtrust-install: create fallback group with ldif file
    
    Currently the framework is used to add the group but we want to avoid
    that users are added explicitly to the group by removing the
    objectclasses groupofnames, ipausergroup and nestedgroup and we want to
    use a name with spaces in it. Both it not easy possible with the
    framework, a LDIF file is used instead to create the group.
    
    Fixes https://fedorahosted.org/freeipa/ticket/3147