vos: print correct command name in diagnostics for changeloc

Fix the label in the diagnostics message, it prints "addsite"
instead of "changeloc" when an error occurs during vos changeloc

Reviewed-on: http://gerrit.openafs.org/5414
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit 1de4561529bdb92b6647a634d9f2c2714e1758e5)

Change-Id: If87fd2a1ed0d4c2975479b5167f6e867db62437a
Reviewed-on: http://gerrit.openafs.org/9431
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>