LU-593 obdclass: echo client for MDS stack

LU-593 obdclass: echo client for MDS stack

1. Add interfaces and tools for exercising a local MDT
   device for performance reasons, in a similar manner
   to obdfilter-survey.
2. add test_create, test_mkdir, test_lookup, test_destroy,
   test_rmdir, test_setxattr, test_md_getattr in lctl for
   md echo client test.

Signed-off-by: Wang di <di.wang@whamcloud.com>
Change-Id: Ibf774a567820ff36b3624e44371c63a9428d82a5
Reviewed-on: http://review.whamcloud.com/1287
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>