bos_util: Fix buffer overflow

Get rid of a buffer overflow in the bos_util utility, by just
printing the key from the 'tbuffer' string, rather than copying
it into 'x' which is too small for it.

Reviewed-on: http://gerrit.openafs.org/9291
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit debf43714b0f00fa00a0ef3384e098de78d28ed6)

Change-Id: If8b075691defeded972d0eff29b7fb594680e433
Reviewed-on: http://gerrit.openafs.org/11018
Reviewed-by: Nathaniel Filardo <nwfilardo@gmail.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>