ORNL-25 process dir page hash collision

ORNL-25 process dir page hash collision

If dir page has hash collision with others, then remove such page
from cache after using to avoid to be found unexpectedly later.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Change-Id: I15ff85e5233248944d77a9d93292d8690e1a715f
Reviewed-on: http://review.whamcloud.com/1234
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>