Coverity defects
    
    The commit b9eeb2e1a8e688dfec753e8965d0e5aeb119e638 for Ticket #481
    "expand nested posix groups" introduced 4 coverity defects.
    
    Description:
    13100, 13101: Missing return statement
    Fix description: addUserToGroupMembership and propogateDeletion-
    UpwardCallback are declared to return an integer value, but
    nothing was returned.  This patch changes it to return 0.
    
    13102: Resource leak
    Fix description: The memory of valueset muid_old_vs is internally
    allocated.  It was meant to be set to muid_upward_vs and freed
    together when muid_upward_vs is freed.  But due to the function
    calling order, it was not properly set and it lost the chance to
    be freed.  This patch calls slapi_attr_get_valueset prior to
    slapi_valueset_set_valueset and let free muid_old_vs together
    with slapi_valueset_set_valueset.
    
    13103: Uninitialized pointer read
    Fix description: Possibly uninitialized variable was passed to
    a logging function slapi_log_error, but actually it was not
    referred.  With this patch, the variable filter is no longer to
    passed to the function.
    (cherry picked from commit e9941a2915ac848abe9a4afe802d0432aa0c354a)