aklog: Protect against overflows from cmdline

The cell, realm and path arrays are populated based on the user's
command line, and xlog_path is populated from their passwd map
entry. Protect against all of these overflowing, by making suitable
use of strlcpy and strlcat.

Caught by coverity (#985764, #985904)

Reviewed-on: http://gerrit.openafs.org/9446
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 2902ef93976fd4baa1a1ed07f4940c5979702856)

Change-Id: I1c8b72aa087902e45cef758844193949471170c5
Reviewed-on: http://gerrit.openafs.org/11060
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>