schema-compat: use libnss_sss.so.2 explicitly to resolve trusted domain users via NSS
    
    When Schema Compatibility plugin is configured to enumerate users and groups
    from Active Directory domains trusted by FreeIPA, use nss_sss module directly
    instead of following nsswitch.conf configuration.
    
    The issue with nsswitch.conf configuration is in the fact that for each request
    all modules in NSS chain are processed while only one of them is responsible
    for users from trusted Active Directory domains, namely, nss_sss.