Resolve conflict AVB rollback index location

Add an `--avb-resolve-rollback-index-location-conflict`
option in merge_target_files. When this option is set,
the merge tool will resolve conflicting index locations
by assigning the smallest unused index location.

This is to support merging system and vendor target files
from two different targets. In this case, the two target
files may have conflict rollback index location because
they were built independently.

Test: atest releasetools_test
Test: validate_target_files *-target_files-*.zip
Test: merge_target_files &&
        add_img_to_target_files &&
        img_from_target_files &&
        flash device
Bug: 300604688
Change-Id: Ibd18ef2a9f3784157fe17966f5364c3c81c9bd9f

tools/releasetools/merge/merge_target_files.py

@@ -90,6 +90,10 @@ Usage: merge_target_files [args]
   --keep-tmp
       Keep tempoary files for debugging purposes.
 
+  --avb-resolve-rollback-index-location-conflict
+      If provided, resolve the conflict AVB rollback index location when
+      necessary.
+
   The following only apply when using the VSDK to perform dexopt on vendor apps:
 
   --framework-dexpreopt-config
@@ -144,6 +148,7 @@ OPTIONS.allow_duplicate_apkapex_keys = False
 OPTIONS.vendor_otatools = None
 OPTIONS.rebuild_sepolicy = False
 OPTIONS.keep_tmp = False
+OPTIONS.avb_resolve_rollback_index_location_conflict = False
 OPTIONS.framework_dexpreopt_config = None
 OPTIONS.framework_dexpreopt_tools = None
 OPTIONS.vendor_dexpreopt_config = None
@@ -230,6 +235,8 @@ def generate_missing_images(target_files_dir):
   ]
   if OPTIONS.rebuild_recovery:
     add_img_args.append('--rebuild_recovery')
+  if OPTIONS.avb_resolve_rollback_index_location_conflict:
+    add_img_args.append('--avb_resolve_rollback_index_location_conflict')
   add_img_args.append(target_files_dir)
 
   add_img_to_target_files.main(add_img_args)
@@ -554,6 +561,8 @@ def main():
       OPTIONS.rebuild_sepolicy = True
     elif o == '--keep-tmp':
       OPTIONS.keep_tmp = True
+    elif o == '--avb-resolve-rollback-index-location-conflict':
+      OPTIONS.avb_resolve_rollback_index_location_conflict = True
     elif o == '--framework-dexpreopt-config':
       OPTIONS.framework_dexpreopt_config = a
     elif o == '--framework-dexpreopt-tools':
@@ -593,6 +602,7 @@ def main():
           'vendor-otatools=',
           'rebuild-sepolicy',
           'keep-tmp',
+          'avb-resolve-rollback-index-location-conflict',
       ],
       extra_option_handler=option_handler)