res/installer:fixed timezone show problem

solve:
    1.only show city in timezone textContent
    2.show UTC+8:00 city in tooltip

tower:https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/e39c9aaa146c4e50b358a4a723f1f9e2/

Change-Id: I1917128d65f30229894474f6fb0d79e0d4fb8a88