qemu: Limit maximum block device I/O tune values

qemu: Limit maximum block device I/O tune values

The values are currently limited to LLONG_MAX which causes some
problems.  QEMU conveniently changed their maximum to 1e15 (1 PB) which
is enough for some time and we need to adapt to that so that we don't
throw "Unknown error" messages.  Strictly limiting these values actually
fixes some corner case values (off-by-one checks in QEMU probably).

Since values out of the new specified range do not overflow anything,
change the type of error as well.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1317531

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>