LUDOC-305 maintenance: handling full/failed OSTs

LUDOC-305 maintenance: handling full/failed OSTs

Improve documentation related to handling full or failing OSTs.

Describe the "osp.*.max_create_count" parameter, and using it to
disable object creation on an OST, rather than deactivating the
OST completely.

Differentiate between disabling an OST for space balancing reasons
and a failing OST.  Add references to QOS space balancing and also
degraded mode for OSTs.

Use "lctl set_param osp.*.active=0" to deactivate the OST rather
than "lctl deactivate", since that is easier for users and they
are functionally equivalent.

Describe the use of "mkfs.lustre --replace" to replace failed OSTs,
rather than the need to backup/restore/binary edit OST config files.

Use proper names for affected sections and cross references, so
that the auto-generated URLs for these sections are useful.

Line-wrap modified sections of text.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I4f253966f463ca1a83d0c7c4efcb22dfc02b6e3f
Reviewed-on: https://review.whamcloud.com/30864
Tested-by: Jenkins
Reviewed-by: Joseph Gmitter <joseph.gmitter@intel.com>