LU-56 ptlrpc: partition data for ptlrpc service

LU-56 ptlrpc: partition data for ptlrpc service

We will have multiple partition data & threads for ptlrpc service,
this patch is the first step work, we moved quite a lot members
of ptlrpc_service to a new structure ptlrpc_service_part.
Now we only create one instance of ptlrpc_service_part for each
service, but we will have multiple instances for each service
very soon (instance per CPT, CPU ParTion).

Signed-off-by: Liang Zhen <liang@whamcloud.com>
Change-Id: I63d816bdf44a22528c6097fe348060f57d862df3
Reviewed-on: http://review.whamcloud.com/2895
Tested-by: Hudson
Reviewed-by: wangdi <di.wang@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>