LU-694 ptlrpc: Job Stats

LU-694 ptlrpc: Job Stats

This feature is to collect filesystem operation stats for the jobs
running on Lustre.

When some job scheduler (SLURM, for instance) is running on lustre
client, the lustre client will pack the job id into each request
(open, unlink, write...), and server will collect those information
then expose them via procfs.

- A 'pb_jobid' is added in 'ptlrpc_body' for storing the jobID;
- The job stats can be accessed from the proc file 'job_stats' in
  each mdt & obdfilter proc entries;
- 'job_cleanup_interval' is created in each mdt & obdfilter proc
  entries for tuning stats cleanup interval;
- 'jobid_var' is created in llite proc entry for configuring the
  jobID environment variable name;

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I35c21f93d7ce1ce648504ce437fcfd374f891453
Reviewed-on: http://review.whamcloud.com/1397
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>