MINOR: map/acl: add the possibility to specify the version in "show map/acl"

MINOR: map/acl: add the possibility to specify the version in "show map/acl"

The maps and ACLs internally all have two versions, the "current" one,
which is the one being matched against, and the "next" one, the one being
filled during an atomic replacement. Till now the "show" commands only used
to show the current one but it can be convenient to be able to show other
ones as well, so let's add the ability to do this with "show map" and
"show acl". The method used here consists in passing the version number
as "@<ver>" before the map/acl name or ID. It would have been better after
it but that could create confusion with keys already using such a format.