lxd-benchmark/benchmark: move from io/ioutil to io and os packages
lxd-benchmark/benchmark: move from io/ioutil to io and os packages

Signed-off-by: Eng Zer Jun <e94bff687675f33b892ede8d3a0a0eab27d6715c@gmail.com>

stgraber/lxd,lxc/lxd,lxc/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,stgraber/lxd