Documented vos restore -creation and -lastupdate

Documented vos restore -creation and -lastupdate

Culled info from commit 21592fe6 by Kris Hees.  These allow
one to specify how to set the creation date and last update
date at volume restore.

Reviewed-on: http://gerrit.openafs.org/4852
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 800a5642a0b9ff514519b4af30b4d0dadd471480)

Change-Id: Ib0d71a34242cdc42753518a454479bccaac0094a
Reviewed-on: http://gerrit.openafs.org/4908
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>