ORNL-13: NonIR client support

ORNL-13: NonIR client support

In this task, NonIR support is added. NONIR clients means those clients who
doesn't know the protocol of imperative recovery. This means they won't be
notified for the restarting of target.

To support NonIR clients, the MGS has to record how many NonIR clients per
file system, and track those clients. In this way, if there are NonIR clients
for a specific file system, the MGS should tell the restarting target to disable
imperative recovery; otherwise, these `old' clients are to be evicted easily.

Signed-off-by: Jinshan Xiong <jay@whamcloud.com>
Change-Id: I3725c66b74d702aa213644ee9a6f89d59b8a8083
Reviewed-on: http://review.whamcloud.com/1218
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>