Check RenderNode's owning view before attaching animators

-Only add animators to a RenderNode when its owning view is attached
-When changing animator's target RenderNode, remove the animator from
 the old target RenderNode that it's currently running on, if any.
Bug: 27141983
Bug: 27145149
Change-Id: I9c9592382d64ecc0390f7ec743a59ce1ad7d9798