EX-3637 osd-ldiskfs: revalidate nonrotational state

EX-3637 osd-ldiskfs: revalidate nonrotational state

Until the nonrotational state of the device is correctly exported by
the underlying storage, periodically recheck the nonrotational state
in case it is changed by the udev/tune_devices.sh script after the
OST is mounted.  It would be possible to check less often (e.g. after
a time limit or some number of operations), but directly checking the
rotational state each time is not more expensive and is only checked
on statfs RPCs (sent about once per 5s from the MDS).

If the nonrotational state is changed and the flash-related cache
parameters have not been explicitly set, then tune them appropriately.

Rename the parameter functions and variables for read_cache_enable,
writethrough_cache_enable, and read_cache_max_filesize to match the
parameter names to make them easier to find in the code.

Lustre-change: https://review.whamcloud.com/45745
Lustre-commit: TBD (from cbc74314532632fbcab88531d43deed7555e125e)

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Iec78a5d5c22c0474eda84a5a793fbb006f3ebbe5
Reviewed-on: https://review.whamcloud.com/45829
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Gaurang Tapase <gtapase@ddn.com>
Tested-by: Gaurang Tapase <gtapase@ddn.com>