releasetools: Fix releasetools_py3_test.

Test: Use a lunch'd target;
      `atest --host releasetools_test releasetools_py3_test`
Change-Id: Ibcced83a7989ef8fc15464728ab1d5fa71ca988e
diff --git a/tools/releasetools/test_check_target_files_vintf.py b/tools/releasetools/test_check_target_files_vintf.py
index a1328c2..79f9018 100644
--- a/tools/releasetools/test_check_target_files_vintf.py
+++ b/tools/releasetools/test_check_target_files_vintf.py
@@ -78,6 +78,8 @@
     for root, _, files in os.walk(test_delta_dir):
       rel_root = os.path.relpath(root, test_delta_dir)
       for f in files:
+        if not f.endswith('.xml'):
+          continue
         output_file = os.path.join(test_dir, rel_root, f)
         with open(os.path.join(root, f)) as inp:
           write_string_to_file(inp.read(), output_file)
diff --git a/tools/releasetools/test_ota_from_target_files.py b/tools/releasetools/test_ota_from_target_files.py
index 9825a5e..f7d59da 100644
--- a/tools/releasetools/test_ota_from_target_files.py
+++ b/tools/releasetools/test_ota_from_target_files.py
@@ -596,7 +596,7 @@
 
     with zipfile.ZipFile(target_file) as verify_zip:
       namelist = verify_zip.namelist()
-      ab_partitions = verify_zip.read('META/ab_partitions.txt')
+      ab_partitions = verify_zip.read('META/ab_partitions.txt').decode()
 
     self.assertIn('META/ab_partitions.txt', namelist)
     self.assertIn('IMAGES/system.img', namelist)
@@ -676,9 +676,9 @@
 
     with zipfile.ZipFile(target_file) as verify_zip:
       namelist = verify_zip.namelist()
-      updated_misc_info = verify_zip.read('META/misc_info.txt')
+      updated_misc_info = verify_zip.read('META/misc_info.txt').decode()
       updated_dynamic_partitions_info = verify_zip.read(
-          'META/dynamic_partitions_info.txt')
+          'META/dynamic_partitions_info.txt').decode()
 
     self.assertIn('META/ab_partitions.txt', namelist)
     self.assertIn('IMAGES/system.img', namelist)