libafs: track dynroot locks for cmdebug

the dynroot dir and symlink locks are not currently tracked;
it would be helpful to know when these locks are in play for tracking
contention

Change-Id: Ibe18586fa5d0ef0e3ea9e7153d79ab64df46ebf3
Reviewed-on: http://gerrit.openafs.org/9997
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>