There are functions from librbd that can use the Timespec type too.
Instead of consuming 'cephfs.Timespec' in the rbd package, create an
internal type that can be exposed through both packages.
This looks a bit like duplication, but it does not break the current
users of Timespec in the cephfs package.
Signed-off-by: Niels de Vos <ndevos@redhat.com>