Calculate verity hash tree.

Calculate verity hash tree in FilesystemVerifierAction based on configs
specified in protobuf, and write it to target partition before reading
from those blocks.

A new error code kVerityCalculationError was added to report error if
it fails.

Bug: 28171891
Test: update_engine_unittests

Change-Id: I492885a0655bf51043902f578720fffd87e6a3cf
diff --git a/payload_state.cc b/payload_state.cc
index c4eb950..36f120a 100644
--- a/payload_state.cc
+++ b/payload_state.cc
@@ -305,6 +305,7 @@
     case ErrorCode::kUnsupportedMajorPayloadVersion:
     case ErrorCode::kUnsupportedMinorPayloadVersion:
     case ErrorCode::kPayloadTimestampError:
+    case ErrorCode::kVerityCalculationError:
       IncrementUrlIndex();
       break;