Avoid adding node itself as child node.

Apps can call addChild through AccessibilityNodeProvider, so it's
possible that an app adds a node itself as a child node. This will break
down the integrity of UI tree and cause failure to operation in
UIAutomator. Thus I suggest do this integrity check when adding child.

Test: as follows
    - built
    - flashed
    - booted
    - run my test script based on uiautomator

Change-Id: I8cba22a1d9d1a49365c6bce4241ef5067502fb79
Signed-off-by: qinyige <qinyige@xiaomi.com>