installer:fixed iframe slideshow load failed

Test:
    disable all loading animation

tower:https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/351c40930d1a461382553f42bf8fc632/
Change-Id: I593a1c52ef5103b213b1d33d8ea4e60bfdfd3c39