Delay bootanimation exit until told to shutdown.

We delay shutting down the animation if there is a boot action present
until we are told by the system to shutdown.

This addresses an issue we are seeing where we switched to a very short
bootanimation (bootanimation_mini.zip) to save CPU but this kills the
boot action prematurely.

Bug: 37992717
Test: Ran locally against imx7d.
Change-Id: I23556b21128b80d08cc55eaa761439a570b8eebe