[incfs] Stream the hash tree for incremental installation

Instead of sending the whole tree upfront use the same
streaming interface for it as for the data blocks

This improves installation speed by almost 200ms,
650-800ms -> 500-600ms

Bug: 153696423
Test: manual, adb install in various configurations

Change-Id: Ia83de2af54ca0b1969397514ea5d761719af9055