revert 208e30f3 and add balloon back
revert 208e30f3 and add balloon back

208e30f3 is workaroud for the bug of the newest qemu at that time.
but the stable qemu(2.4.1) doesn't have such bug.

revert it. sigh...

Signed-off-by: Lai Jiangshan <b337eedf453972390e4695e362aeea2634ef4e0c@gmail.com>

wrouesnel/runv,gao-feng/runv,hyperhq/runv,jinfenw/runv,jinfenw/runv,hyperhq/runv,feiskyer/runv,gnawux/runv,bergwolf/runv,gnawux/runv,gao-feng/runv,hyperhq/runv,feiskyer/runv,jinfenw/runv,bergwolf/runv,wrouesnel/runv,YaoZengzeng/runv,laijs/runv,gnawux/runv,laijs/runv,laijs/runv,YaoZengzeng/runv,bergwolf/runv,gao-feng/runv