Supply apex_info.pb as parameter to delta_generator if file exists

Supply generator with parameter --apex_info_file=META/apex_info.pb
if the file exists.

This ensures that apex_info is included in payload header.

This is identical to the behaviour of brillo_update_payload
which is not being used since:
Invoke delta_generator directly
fcd731e3d6

Issue: 286253576
Test: Manual, confirm that apex_info is included in payload header
Change-Id: Ic096c5f8966beec8686f918aba462c955290a6c5

tools/releasetools/ota_utils.py

@@ -846,6 +846,11 @@ class PayloadGenerator(object):
     if os.path.exists(dynamic_partition_info):
       cmd.extend(["--dynamic_partition_info_file", dynamic_partition_info])
 
+    apex_info = os.path.join(
+      target_dir, "META", "apex_info.pb")
+    if os.path.exists(apex_info):
+      cmd.extend(["--apex_info_file", apex_info])
+
     major_version, minor_version = ParseUpdateEngineConfig(
         os.path.join(target_dir, "META", "update_engine_config.txt"))
     if source_file: