Ticket 47592 - automember plugin task memory leaks
    
    The search pblock was not destroyed at the end of the export and rebuild
    tasks.
    
    https://fedorahosted.org/389/ticket/47592
    
    Reviewed by: richm(Thanks!)
    (cherry picked from commit 085c6d494f90231f2e572a668ab601c321bffb01)
    (cherry picked from commit c9c7d545a987f8f52c9752ba1181d1885b74480c)