LU-3642 seq: make seq_proc_write_common() safer

LU-3642 seq: make seq_proc_write_common() safer

Don't allow seq_proc_write_common() to specify arbitrary ranges,
since this can permanently corrupt the sequence controller and/or
sequnece server.  That would allow duplicate FID allocation, or
possibly prevent any new files to be created or servers to be added
to the filesystem.

Instead, limit the sequence range that can be written via /proc to
a subset of the sequence range currently allocated to that node.
Add the "clear" keyword to allow dropping the entire local sequence
and force a new one to be fetched from the sequence server.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I89da0223a52ce8bec787b1d5099402c84274291a
Reviewed-on: http://review.whamcloud.com/7123
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Hudson
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>