Fix memory leak in openvz_conf.c
    
    If there is no error while executing a function "openvzParseBarrierLimit"
    a "str" string where is duplicate of a "value" string isn't freed and it
    leads into memory leak.
    
    This has been found by coverity.
    
    Signed-off-by: Pavel Hrdina <phrdina@redhat.com>