LU-106 procfs: many proc entries are not accessed safely

LU-106 procfs: many proc entries are not accessed safely

Some in memory data may be released/uninitialized at the time
of proc entry creation/removal, this patch includes the following
fixes:
* initialize data before proc entry creation
* free data after proc entry removal
* free proc entries in obd_precleanup() because
  obd_uuid/nid/nid_stats_hash are released in class_cleanup().
* free proc entries after obd_zombie_barrier() because obd_export
  hold one refcound of nid_stat.
* check osd->od_mount before accessing osd proc entries because the
  osd proc entries are created before mount.

Signed-off-by: Lai Siyao <laisiyao@whamcloud.com>
Change-Id: I03cb977e1be0747032a70f6a39fec804f81d70cc
Reviewed-on: http://review.whamcloud.com/326
Tested-by: Hudson
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>