Since instances can be started, failed over and migrated with less than
their maximum memory N+1 will use the minimum memory for verification.

Note that this accounts only for the instances being moved being
resized, and not for the ones already on the node, as ganeti will not
automatically resize other instances on the target node now when trying
to start/failover/migrate an instance.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>