staging: lustre: llite: enforce pool name length limit

The pool related codes have some inconsistency about the length
of pool name. Creating and setting a pool name of length 16
to a directory will succeed. However, creating a file under
that directory will fail.

This patch disables any pool name which is longer or equal to
16. And it changes LOV_MAXPOOLNAME from 16 to 15 which might
cause some invalid LLOG records of OST pools with 16 byte names.
It is not a problem since invalid LLOG records are just ignored.
And OST pools with 16 byte names won't work well anyway on the
old versions. There will be problem of inconsistency if part of
the servers have this patch and part of the servers don't. But
it would be safe to assume that this is not a normal
configuration.

Signed-off-by: Li Xi <lixi@ddn.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5054
Reviewed-on: http://review.whamcloud.com/10306
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>