LU-11963 osd: Add nonrotational flag to statfs

LU-11963 osd: Add nonrotational flag to statfs

It is potentially useful for the MDS and userspace to
know whether or not an OST is using non-rotational media.

Add a flag to obd_statfs that reflects this.

Users can override this parameter in proc.

ZFS does not currently make this information available to
Lustre, so default to rotational and allow users to
override.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Iac2b54c5d8cc1eb79cdace764e93578c7b058661
Reviewed-on: https://review.whamcloud.com/34235
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>