installer:limit username length <= 32

tower:https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/9b2cf489661f4b369c1a39d56ad5c5a4/#a5fa5e864bd24563943826a8a1e87633
Change-Id: I23f89dbeed349b57ad7ddd6f83122c8c8ccda0a2