LU-13258 obdclass: bind zombie export cleanup workqueue

LU-13258 obdclass: bind zombie export cleanup workqueue

Lustre uses a workqueue to clear out stale exports. Bind this
workqueue to the cores used by Lustre defined by the CPT setup.

Move the code handling workqueue binding to libcfs so it can be
used by everyone.

Rename CONFIG_LUSTRE_PINGER to CONFIG_LUSTRE_FS_PINGER to match
linux client.

Change-Id: Ifa109f6a93e6ec6bbdef5e91fe8ca1cde0eaea3e
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/38212
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>