Reduce boot animation completion check interval

- 200 ms interval can increase boot time by 200ms.
- Reduce it to 50 ms for now.
- TODO: Migrate to SystemServices.waitForState and remove
  polling completely

Bug: 157281833
Bug: 159045990
Test: reboot and check boot time
Change-Id: I2a7b7da90f1b14c16a7429ebd7f2971792f48e3c