LU-12036 ofd: add "no_precreate" mount option

LU-12036 ofd: add "no_precreate" mount option

Add a mount option to disallow object creation on the OST.  That
allows an OST to be mounted by the administrator without it being
immediately available for use by clients/applications.  This may
be useful if the OST needs to be added to a specific pool first,
or if it is being debugged or similar.

Mount option can be disabled with the obdfilter.*.no_precreate
tunable parameter.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Icdb64a4bdd5a66b0e9e6d483e3113b97d53ebbe5
Reviewed-on: https://review.whamcloud.com/36716
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>