support schema files from third-party plugins
    
    Allow upgrade process to include schema files from third-party plugins
    installed in /usr/share/ipa/schema.d/*.schema.
    
    The directory /usr/shar/eipa/schema.d is owned by the server-common
    subpackage and therefore third-party plugins should depend on
    freeipa-server-common (ipa-server-common) package in their package
    dependencies.
    
    Resolves: https://fedorahosted.org/freeipa/ticket/5864
    Reviewed-By: Martin Basti <mbasti@redhat.com>