LU-448 add lst stat --count

LU-448 add lst stat --count

This adds lst stat --count, making it easier to script up data
collection for performance tests.

The patch is from Oracle bug 22638 attachment 33001

Change-Id: I46aa1de12ea8e6c2d5eafff8ce5c31d7d618c06f
Signed-off-by: Wally Wang <wang@cray.com>
Reviewed-on: http://review.whamcloud.com/1004
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Liang Zhen <liang@whamcloud.com>
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>