ConvertROtoRW: Use old copyDate for creationDate

ConvertROtoRW: Use old copyDate for creationDate

When we convert an RO volume to an RW, currently we just copy the
copyDate and creationDate from the RO metadata into the RW. But the
copyDate and creationDate fields have different meanings for RW and RO
volumes: for ROs, the creationDate is merely the last time the data
was updated from the RW during a release operation.

So, if the copyDate is older than the creationDate, use the copyDate
as the new RW creationDate instead. This will probably not match the
creationDate of the original RW, but it will be closer to it, and it
will more accurately represent the conceptual "created time" of the
new RW.

Doing this can avoid forcing an unnecessary full dump on a subsequent
release of the resultant RW volume, since the creationDate is more
accurate.

Reviewed-on: http://gerrit.openafs.org/3891
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit f47487db051ba6b51ae12daf7edc09ecfd3c38cd)

Change-Id: I54516a20ebb87d9c482cbc4840e0d236e7c54f8a
Reviewed-on: http://gerrit.openafs.org/5755
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>