LU-3319 procfs: update shared server side core proc handling to seq_files

LU-3319 procfs: update shared server side core proc handling to seq_files

Several of the server side abstact layers such as mdt,mgs
etc share several common proc handling routines. This patch
adds the seq_file version so that the stack can gradually
be ported over to these new methods.

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I2dd64046fdd4d2bb6f7550bb49cf1c9ef703c157
Reviewed-on: http://review.whamcloud.com/7933
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>