lxd/storage: Check for kernel support and O_DIRECT flag before setting direct IO
lxd/storage: Check for kernel support and O_DIRECT flag before setting direct IO

Signed-off-by: Evan Z Seils <c747f58c32d495e33833fc73f17f763ffc222af5@gmail.com>

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