Add trusconfig-show and trustconfig-mod commands
    
    Global trust configuration is generated ipa-adtrust-install script
    is run. Add convenience commands to show auto-generated options
    like SID or GUID or options chosen by user (NetBIOS). Most of these
    options are not modifiable via trustconfig-mod command as it would
    break current trusts.
    
    Unit test file covering these new commands was added.
    
    https://fedorahosted.org/freeipa/ticket/3333