Currently, DELETE service sets tombstone expiration epoch to
`current epoch + 5`. This works less than ideal in private networks
where an epoch can be e.g. 10 minutes. In this case, after a node is
unavailable for more than 1 hour, already deleted objects have a chance
to reappear.
After this commit tombstone lifetime can be configured.
Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
