shutown:fixed some bug of switch_user

1.update switch_user icon
2.fixed the bug that the switch_user icon must be hiden when user.length < 2
3.fixed that the icons arenot in the center of screen when switch_user icon shows

Change-Id: Ic544ebf1cbd2917241e741765143c8ebef312bce
Merge "shutown:fixed some bug of switch_user"